Elementary Processes

in Solids and at Interfaces:

Carrier, Lattice, and Molecular Dynamics

International workshop on

Kloster Banz

Bad Staffelstein, Germany

May 29 - June 1, 2011

Welcome Address

Dear participant,

We are delighted to welcome you to this workshop on

Elementary Processes in Solids and at Interfaces:Carrier, Lattice and Molecular DynamicsKloster Banz, Bad StaUelstein (Germany), May 29 – June 1, 2011

It gathers a scientiVc community working in the Velds of ultrafast condensed matter and surfacescience in order to address fundamental aspects of these adjacent and overlapping areas. Thisjoint expertise promises a creative and dynamic environment to discuss ultrafast dynamics andelementary processes deVning the functional properties of solids, surfaces, and interfaces. Theseinvolve ultrafast lattice and carrier dynamics, coupling of electronic, phononic, and moleculardegrees of freedom as well as strong correlation eUects in solids. We are looking forward tolively discussions that help to identify future challenges and develop strategies to tackle these.

We hope that you will have a pleasant time and enjoy both the exciting science and the beautifulvenue: Kloster Banz, a Benedictine abbey above the river Main in Franconia.

Many thanks for coming,

Martin Wolf Julia Stähler

Contents

Welcome Address 3

ScientiVc Program 6

Abstracts 11Invited Speakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Poster Abstracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

List of Participants 67

Notes 74

ScientiVc Program

Sunday, May 29

Welcoming SessionChair: Martin Aeschlimann

16.45 Martin WolfWelcome Address

17.00 Martin Weinelt (30+5)Two-State Double-Continuum Fano Resonance at the Silicon(100)-Surface

17.35 Dwayne Miller (30+5)"Making the Molecular Movie": First Frames. . . Coming Features

18.10 Andrea Cavalleri (30+5)Controlling Superconductivity with Light

19.00 Dinner

20.30 Poster Session I

Monday, May 30

Strong Correlations and Photoinduced Phase TransitionsChair: Uwe Bovensiepen

8.30 Rupert Huber (30+5)Sub-Cycle Dynamics and Terahertz Control of Low-Energy Excitations

9.05 Dirk Manske (30+5)Density-Matrix Theory for Time-Resolved Dynamics of Superconductors in Non-Equilibrium

9.40 Luca Perfetti (30+5)Dynamics of the Electrons and Coherent Phonons in Photoexcited Bismuth

10.15 CoUee break

10.40 Angel Rubio (30+5)Modelling Photo-Induced Dynamical Processes in Complex Nanostructures and Oxides: Role ofElectron Correlations, Dynamical Screening and Electron-Phonon Coupling

11.15 Patrick Kirchmann (20+5)Separating the Dynamics of Spin and Charge-Ordered Phases in the Nickelates Using Time-ResolvedSoft X-Ray DiUraction

11.40 Michael Bauer (30+5)Dynamics in Correlated Materials Probed by Femtosecond XUV Photoemission

12.30 Lunch

Molecules on Surfaces: Functionality and DynamicsChair: Julia Stähler

14.00 Karina Morgenstern (30+5)Single Molecule Manipulation by Light and Electrons

14.35 Petra Tegeder (30+5)Optically and Thermally Induced Switching of Molecules on Metal Surfaces

15.10 Karsten Reuter (30+5)Adsorption of aromatic molecules: Tackling the Van der Waals Challenge with DFT-D?!

15.45 Leonhard Grill (20+5)Study and Manipulation of Single Functional Molecules on Surfaces

16.10 CoUee break

16.35 Xiaoyang Zhu (30+5)Exciton Fission and Dissociation at Organic Semiconductor Interfaces

17.10 Christian Frischkorn (20+5)Ferroelectric Ordering and Spin Polarization of Thin Adsorbate Layers on Metal Surfaces

17.35 Peter Saalfrank (30+5)Non-Adiabatic Molecular Dynamics at Metal Surfaces

18.10 Ulrich Höfer (30+5)Ultrafast Electron Dynamics at Metal-/Organic Interfaces

19.00 Dinner

20.30 Poster Session II

7

Tuesday, May 31

Recent Developments in Ultrafast ScienceChair: Ulrich Höfer

8.30 Reinhard Kienberger (30+5)Attosecond Spectroscopy on Solids

9.05 Anders Nilsson (30+5)Ultrafast Studies of Bonding Rearrangements in Adsorbed CO on Ru Probed with LCLS

9.40 Alfred Leitenstorfer (30+5)Femtosecond Nanophotonics: Single Electrons, Photons and Sub-Cycle ConVnement of Light in FourDimensions

10.15 Ralph Ernstorfer (20+5)Lightwave-Control of Electronic Motion in the Solid State

10.40 CoUee break

11.05 Lukasz Piatkowski (20+5)Ultrafast Dynamics of Interfacial Water Revealed by 2-Dimensional Surface Vibrational Spec-troscopy

Young Investigator SessionChair: Reinhard KienbergerSpeakers will be selected by the YIS committee from posters.

11.30 t. b. a. (20+5)

11.55 t. b. a. (20+5)

12.20 t. b. a. (20+5)

12.45 Lunch

14.00 Excursion

Celebratory Evening SessionChair: Hrvoje Petek

19.00 Conference Dinner

20.30 Margaret Murnane (30+5)Bright Coherent Attosecond Kiloelectronvolt X-ray Supercontinua and Applications in Nanoscienceand Nanotechnology

21.05 Pedro Echenique (30+5)Electron Dynamics at Surfaces and Nanostructures

21.40 Drinks and discussion

8

Wednesday, June 1

Low Dimensional Systems and Spin DynamicsChair: Alfred Leitenstorfer

8.30 Martin Aeschlimann (30+5)Ultrafast Optical Control of Magnetism at the Nanoscale

9.05 Tobias Kampfrath (20+5)Nonlinear Terahertz Spectroscopy of Magnetically Ordered Solids

9.30 Alexey Melnikov (20+5)Experimental Approach for Investigation of Spin Dynamics Excited by Femtosecond Pulses ofSpin-Polarized Hot Carriers

9.55 CoUee Break

10.20 Uwe Bovensiepen (30+5)Decay of Hot Quasi-Particles in Two-Dimensional Materials

10.55 Hrvoje Petek (30+5)Exploring the Electronic Structure and Dynamics in the Inner Space of 0D-2D Hollow Molecules bySTM, 2PP, and Theory

11.30 Tobias Hertel (30+5)Radiative and Non-Radiative Decay in Carbon Nanotubes

12.05 Tony F. Heinz (30+5)Seeing Electrons in Two Dimensions: Optical Spectroscopy of Graphene

12.45 Lunch and Departure

9

Abstracts

Invited Speakers

Sunday, May 29, 17.00–17.35 Martin Weinelt (30 + 5)

Two-State Double-Continuum Fano Resonance at theSilicon(100)-Surface

Martin Weinelt, Christian EickhoU, Martin Teichmann

Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 BerlinMax-Born-Institut, Max-Born-Straße 2A, 12489 Berlin, Germany

The Fano eUect originates from quantum interference of competing optical paths when a discreteexcited electronic state couples to continuum excitations. Interference requires phase coherence whichin the solid state is rapidly destroyed upon electron scattering. Here we show that Fano resonancescan be observed on a bare silicon surface at room temperature. Combining ultrafast laser excitationand photoelectron spectroscopy we follow the optical transition between the dangling-bond and image-potential-surface bands on Si(100) which are degenerate with the silicon valence and conduction band,respectively. Tuning the photon energy across the surface resonance reveals asymmetric line-proVlesin the two-photon photoelectron yield of both initial- and intermediate states. This two-dimensionalinterference pattern is analyzed in the energy domain by an analytic extension of Fano’s model and inthe time domain solving optical Bloch equations. The observed two-state double-continuum interferencephenomena strongly modify the photo-absorption at surfaces and are of general importance for lightconversion in nanostructures and light-harvesting devices.

[1] U. Fano, Sullo spettro di assorbimento dei gas nobili presso il limite dello spettro d’arco, Nuovo Cimento12, 154 (1935)

[2] U. Fano, EUects of conVguration interaction on intensities and phase shifts, Phys. Rev. 124, 1866 (1961)

12

Dwayne Miller (30 + 5) Sunday, May 29, 17.35–18.10

"Making the Molecular Movie":First Frames. . . Coming Features

R. J. Dwayne Miller 1,2

1Max Planck Research Group for Atomically Resolved Dynamics, Department of Physics, University ofHamburg, Centre for Free Electron Laser Science/DESY

2Departments of Chemistry and Physics, University of Toronto

Femtosecond Electron DiUraction has enabled atomic resolution to structural changes as they occur,essentially watching atoms move in real time directly observe transition states. This experiment has beenreferred to as "making the molecular movie" and has been previously discussed in the context of a gedankenexperiment. With the recent development of femtosecond electron pulses with suXcient number density toexecute single shot structure determinations, this experiment has been Vnally realized. A new concept inelectron pulse generation was developed based on a solution to the N-body electron propagation probleminvolving up to 10,000 interacting electrons that has led to a new generation of extremely bright electronpulsed sources that minimizes space charge broadening eUects. Previously thought intractable problemsof determining t=0 and fully characterizing electron pulses on the femtosecond time scale have now beensolved through the use of the laser pondermotive potential to provide a time dependent scattering source.Synchronization of electron probe and laser excitation pulses is now possible with an accuracy of 10femtoseconds to follow even the fastest nuclear motions. The camera for the "molecular movie" is nowin hand. Several movies depicting atomic motions during passage through structural transitions willbe shown. Atomic level views of the simplest possible structural transition, melting, will be presentedfor a number of systems in which both thermal and purely electronically driven atomic displacementscan be correlated to the degree of directional bonding. Optical manipulation of charge distributions andeUects on interatomic forces/bonding can be directly observed through the ensuing atomic motions. Newphenomena involving strongly correlated electron systems will be presented in which an exceptionallycooperative phase transitions has been observed. The primitive origin of molecular cooperativity has alsobeen discovered in recent studies of molecular crystals. These new developments will be discussed in thecontext of developing the necessary technology to directly observe the structure-function correlation inbiomolecules the fundamental molecular basis of biological systems.

13

Sunday, May 29, 18.10–18.45 Andrea Cavalleri (30 + 5)

Controlling Superconductivity with LightAndrea Cavalleri1,2

1Max Planck Research Department for Structural Dynamics, University of Hamburg2 Department of Physics, University of Oxford

In this talk, I will discuss our recent progress in the control of superconductivity in High Tc Cuprates.Rather than using radiation at visible wavelengths, we focus on excitations in the mid-IR, near 15 THz, orin the far IR, between 1 and 2 THz.

I will discuss a number of experiments in which we have used mid-infrared radiation to inducesuperconductivity in the striped ordered compoundLa1.675Eu0.2Sr0.125CuO4, in which we have observe the emergence of coherent transport on remarkablyfast timescale. I will also describe more recent experiments in which single cycle, sub-1THz Velds have beenused to modulate the interlayer tunneling strength in the superconducting compound La1.84Sr0.16CuO4,driving ultrafast non-dissipative oscillations between resistive and superconducting states. Thirdly, I willdiscuss experiments in which Narrowband THz radiation from a Free Electron Laser is used to exciteintrinsically localized vortices, which are detected in the time domain by THz electromagnetically inducedtransparency.

Finally, I will discuss experiments in which synchrotron and Free Electron Laser soft x-ray radiationis used to measure charge and spin order and how this will bring important new information on thedynamic formation of a superconducting state.

Dinner at 19.00.Postersession I at 20.30.

14

Rupert Huber (30 + 5) Monday, May 30, 8.30–9.05

Sub-Cycle Dynamics and Terahertz Control ofLow-Energy Excitations

R. Huber1,2

1Department of Physics, University of Konstanz, 78464 Konstanz, Germany2Department of Physics, University of Regensburg, 93040 Regensburg, Germany

Ultrafast phenomena involving low-energy elementary excitations play a key role in condensed matterphysics. Examples range from phonons, magnons, and intermolecular vibrations to superconductingenergy gaps. Few-cycle pulses in the terahertz spectral domain have been advanced to monitor [1] andcontrol [2] this dynamics directly with femtosecond resolution.In a Vrst set of experiments, we combine ellipsometry and ultrabroadband THz pump-probe schemesto trace superconducting and spin-density wave gaps after photoexcitation of the pnictide compoundBa(Fe,Co)2As2. Furthermore few-cycle multi-THz transients with peak electric Velds exceeding 10 GV/m[3] set the stage for nonlinear optics mediated by electric [2] and magnetic [4] coupling. Here two-dimensional multi-wave mixing with high-Veld THz transients is observed in the semiconductor indiumantimonide. This scheme paves the way towards studies in various systems ranging from intermolecularvibrations to coherent gap dynamics in unconventional superconductors. Finally intense THz transientsserve as a femtosecond bias of semiconductors at Velds far beyond the quasistationary threshold fordielectric breakdown. Few-cycle NIR pulses synchronized to the THz transients on an attosecond timescaleprobe interband transitions in the extreme strong-Veld limit of the Franz-Keldysh eUect, with sub-cycleprecision. Further investigations into a broad range of high-Veld eUects in semiconductors are under way,bringing the observation of phenomena such as Bloch oscillations in bulk semiconductors, into reach.

[1] see e.g. R. Huber et al., Nature 414, 286 (2001), G. Günter et al., Nature 458, 178 (2009), A. Pashkin etal., Phys. Rev. Lett. 105, 067001 (2010).

[2] S. Leinß et al., Phys. Rev. Lett. 101, 246401 (2008).

[3] A. Sell et al., Opt. Lett. 33, 2767 (2008).

[4] T. Kampfrath et al., Nature Photonics 5, 31 (2011).

15

Monday, May 30, 9.05–9.40 Dirk Manske (30 + 5)

Density-Matrix Theory for Time-Resolved Dynamics ofSuperconductors in Non-Equilibrium

Dirk Manske

Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany

We study the ultrafast dynamics of unconventional superconductors from a microscopic viewpointemploying density-matrix theory. In particular, we can treat the oscillations of the superconductingorder parameter exactly and are able to describe the elementary excitations after a strong pump pulse.Furthermore, using a cluster expansion method, we derive and solve numerically equations of motionsfor the case that damping due to phonons is important [1]. Our theory is partly able to describe time-resolved pump-probe Raman experiments in the high-𝑇𝑐 cuprates in which optical phonons play acharacteristic role [2,3]. Finally, we extend our theory to 2-band superconductors which is motivated byrecent time-resolved experiments in the iron-based superconductors [4].

[1] J. Unterhinninghofen, D. Manske, and A. Knorr, Phys. Rev. B 77, 180509(R) (2008).

[2] R. P. Saichu et al., Phys. Rev. Lett. 102, 177004 (2009).

[3] A. Schnyder and D. Manske, preprint (2011).

[4] A. Akbari, I. Eremin, and D. Manske, in preparation.

16

Luca Perfetti (30 + 5) Monday, May 30, 9.40–10.15

Dynamics of the Electrons and Coherent Phonons inPhotoexcited Bismuth

L. Perfetti, I. Reshetnyak, A. Van Roekhegem, J. Faure1, E. Papalazarou, J. Mauchain, M.Marsi2

1Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS-CEA/DSM, 91128 Palaiseau Cedex, France,2Laboratoire de Physique des Solides, Université Paris Sud, CNRS-UMR8502, 91405 Orsay, France

We investigate the bulk and surface states of photoexcited Bismuth by means of time resolved photo-electron spectroscopy. Our results indicate that the binding energy of bulk electronic states is modulatedby the temporal evolution of the 𝐴1𝑔 phonon mode. The oscillation period of the photoexcited modeis in excellent agreement with time resolved x-ray scattering and transient reWectivity. In addition, thecoupling between a bulk state and the coherent phonon strongly depends on the the electronic wavevectorand band index. As expected, the surface electronic states have weaker coupling to the coherent phonons.Nonetheless, we observe a photoinduced replica of a this band in proximity of the Fermi level crossing.Possible explanations of this exotic excitation will be discussed.

CoUee break from 10.15 to 10.40.

17

Monday, May 30, 10.40–11.15 Angel Rubio (30 + 5)

Modelling Photo-Induced Dynamical Processes inComplex Nanostructures and Oxides:

Role of Electron Correlations, Dynamical Screening andElectron-Phonon Coupling

Angel RubioNanoBio Spectroscopy Group, Departamento de Física de Materiales, Universidad del País Vasco. EuropeanTheoretical Spectroscopy Facility (ETSF), EdiVcio Korta, Avda. Tolosa 72, 20018 San Sebastián, Spain.

Within the goal of spanning larger time-scales and more complex structures, we will describe a newmethod to mimic the electron-ion dynamics within the Ehrenfest scheme where no explicit orthog-onalization is necessary and we can increase of the time step while keeping the system close to theBorn-Oppenheimer surface. The method is easily implemented and scales very well with the systemsize. Applications to the excited state dynamics in some organic molecules will be used as text cases toillustrate the performance of the approach. We will present the dynamical prcesses in organic/inorganiccharge-transfer systems and biologial complexes. In particular we will show the eUect of electron-holeattraction in those systems. Pros and cons of present functionals will be highlighted and provide insightin how to overcome those limitations by merging concepts from many-body perturbation theory andtime-dependent density functional theory. All those developments constitute a basic ingredient for therealization of the European Theoretical Spectroscopy Facility (ETSF, http://etsf.eu) as a top-level scientiVcinfrastructure.

18

Patrick Kirchmann (20 + 5) Monday, May 30, 11.15–11.40

Separating the Dynamics of Spin and Charge-OrderedPhases in the Nickelates

Using Time-Resolved Soft X-Ray DiUractionP. S. Kirchmann2, Y. D. Chuang1, W. S. Lee2, R. G. Moore2, L. Patthey2,3, M. Trigo5,

D. H. Lu4, M. Yi2, O. Krupin6,9, M. Langner7, N. Huse7, J. Robinson7, Y. Chen2, Y .Zhu7,S. Zhou1,7, D. Reis5 R. A. Kaindl7 R. W. Schoenlein1,7, D. Doering8, P. Denes8, W. F.Schlotter9, J. J. Turner9, S. L. Johnson3, M. Först10, T. Sasagawa11, T. P. Devereaux2,

Z.-X. Shen2, Z. Hussain1

1 ALS, Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA, USA2 SIMES, Stanford Institute for Energy and Material Science, SLAC National Accelerator Laboratory and

Stanford University, Menlo Park, CA, USA3 SLS, Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland

4 SSRL, Stanford Synchrotron Radiation Light Source, SLAC National Accelerator Laboratory, Menlo Park,CA, USA

5 PULSE, Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory, Menlo Park, CA,USA

6 The European X-Ray Laser Project XFEL, Hamburg, Germany7 Material Science Division, Lawrence Berkeley Laboratory, Berkeley, CA, USA

8 Engineering Division, Lawrence Berkeley Laboratory, Berkeley, CA, USA9 LCLS, Linear Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, CA, USA10 Max-Planck Research Group for Structural Dynamics, University of Hamburg, CFEL, Germany

11 Tokyo Institute of Technology, Materials and Structure Laboratory, Japan

Striped phases can emerge in charge-doped Mott insulators [1], segregating spin and charge degrees offreedom into nanoscale domains, where one dimensional rivers of charge serve as anti-phase domain wallsbetween anti-ferromagnetic spin domains. While the equilibrium properties for stripe-ordered materialslike Cuprates [2] and Nickelates [3] have been intensely studied, the challenge to identify the driving forceof spin and charge separation remains. Femtosecond time-resolved pump-probe diUraction experiments[4] provide a natural approach to disentangle the strongly coupled charge, spin, and lattice degrees offreedom. We performed time-resolved 800 nm-optical-laser-pump and resonant-soft-x-ray-diUraction-probe experiments at the x-ray free electron laser (XFEL) at the Linear Coherent Light Source (LCLS) [5]on a stripe phase nickelate (La1.75Sr0.25NiO4) at the Ni-L3 edge. Surprisingly, the spin order (SO) is lesssusceptible to optical excitation and survives even when the charge order (CO) is absent, despite its lowerthermodynamic transition temperature. While the SO initially recovers faster than the CO, its asymptoticbehavior suggests a second and much longer time scale for full relaxation. From a technical point of view,our experiment demonstrates the feasibility of applying the intense XFEL pulse to study the electronicand magnetic states of solids via ultrafast time-resolved optical-pump x-ray probe spectroscopy.

[1] Zaanen,J. et al., Phys. Rev. B 40, 7391 (1989)

[2] Tranquada,J. M. et al., Nature 375, 561 (1995).

[3] Chen,C. H. et al., Phys. Rev. Lett. 71, 2461 (1993).

[4] Trigo, M. et al., MRS Bulletin 35, 514 (2010).

[5] Emma,P. et al., Nature Photonics 4, 641 (2010).

19

Monday, May 30, 11.40–12.15 Michael Bauer (30 + 5)

Dynamics in Correlated Materials Probed byFemtosecond XUV Photoemission

Michael Bauer

Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24118 Kiel,Germany

The combination of ultrafast light sources in the UV spectral regime and the technique of photoelectronspectroscopy provides a unique tool for a most direct access to ultrafast processes in condensed mattersystems that couple to electronic degrees of freedom. Angular resolution enables one in this context tomonitor the temporal evolution of the valence electronic band structure of a solid at selected—and possiblycritical—points in momentum space [1]. The application of XUV photon pulses enlarges the accessiblemomentum regime considerably so that band structure transients within the entire Vrst Brillouin zone oreven beyond can be recorded [2].

In this talk I will report about a time-resolved XUV photoemission study on the laser-induced meltingof a charge-density wave (CDW) state in the transition-metal dichalcogenide 1T-TiSe2. Distinct transientspectral changes at the corner of the Vrst Brillouin zone enable us to observe the extremely fast (sub-30fs) collapse of long-range order associated with the CDW phase. We show that the built up of screeningbecause of the transient generation of free carriers accounts for the observed timescale, and particularlyits dependence on the excitation Wuence.

[1] F. Schmitt et al., Science 321, 1649 (2008).

[2] S. Mathias et al., Rev. Sci. Instr. 78, 083105 (2007).

Lunch break from 12.30 to 14.00.

20

Karina Morgenstern (30 + 5) Monday, May 30, 14.00–14.35

Single Molecule Manipulation by Light and ElectronsKarina Morgenstern

Division of Atomic and Molecular Structures (ATMOS)Leibniz University of Hannover

Germany

The development of molecular switches on the single molecule level is a major challenge on the pathtowards incorporating molecules as building units into nanoelectronic circuits. Azobenzene derivativesare a prototype class of molecules that are well known to switch in the gas phase under illumination basedon a cis-trans isomerization. With a scanning tunneling microscope (STM) it is also possible to induce thischemical reaction on an individual molecule by electrons tunneling inelastically from the STM tip into amolecule. We explored several azobenzene derivatives, p-hydroxy-azobenzene, amino-nitro-azobenzene,and anilino-nitro-azobenzene on a variety of surfaces, Cu(111), Ag(111), Au(111), and NaCl/Ag(111) bothwith respect to electron induced and to light induced isomerisation. From these studies we deduce generalrules for the feasibility of the use of azobenzene derivatives within nanoelectronic circuits.

21

Monday, May 30, 14.35–15.10 Petra Tegeder (30 + 5)

Optically and Thermally Induced Switching ofMolecules on Metal Surfaces

Petra Tegeder

Freie Universität Berlin, Institut für Experimentalphysik, Arnimallee 14,D-14195 Berlin/Germany

Understanding the switching ability of molecules on surfaces upon excitation with external stimuli is aprerequisite for the development of functional molecular devices with possible applications to informationprocessing, storage, or switching. While the switching mechanisms in many classes of molecular switchesare thoroughly studied and understood in solution, their counterparts on surfaces still remain largelyunresolved. In particular, many switching processes are suppressed or irreversible when the molecules areanchored to a metallic substrate. The adsorption conVguration and steric hindrance are only one factorinWuencing the switching capability. More important is the electronic coupling strength between adsorbateand substrate and accordingly the lifetime of molecular excited states which is signiVcantly reduced atmetal surfaces. I will discuss several examples of optically and thermally induced conformational changesin molecular switches at noble metal surfaces [1–4].

[1] M. Wolf, P. Tegeder, Surf. Sci., 603, 1506 (2009).

[2] M. Piantek et al., J. Am. Chem. Soc., 131, 12729 (2009).

[3] F. Leyssner et al., J. Phys. Chem. C, 114, 1231 (2010).

[4] J. Mielke et al., ACS Nano, in press (2011).

22

Karsten Reuter (30 + 5) Monday, May 30, 15.10–15.45

Adsorption of aromatic molecules:Tackling the Van der Waals Challenge with DFT-D?!

Karsten Reuter

Dept. of Chemistry, Technische Universität München,Lichtenbergstr. 4, D-85747 Garching (Germany)

The potential of a future molecular electronics has motivated many studies of functional organicmolecules at metal surfaces. For Vrst-principles theory it is particularly the possibly signiVcant contri-bution of dispersive van der Waals (vdW) interactions in the molecule-substrate interaction that limitsthe common workhorse for large-scale calculations, density-functional theory (DFT) with semi-localexchange and correlation functionals. As higher-level theories including non-local vdW interactions byconstruction are presently barely tractable for corresponding system sizes, Vrst insight could come fromcomputationally inexpensive semi-empirical dispersion correction (DFT-D) schemes. There are relativelygood reasons not to use present DFT-D formulations for adsorption at metal surfaces though. Using theadsorption of the molecular switch azobenzene at coinage metal surfaces as a case in point I will showthat it sometimes doesn’t hurt to proceed nevertheless [1,2].

[1] G. Mercurio et al., Phys. Rev. Lett. 104, 036102 (2010).

[2] E.R. McNellis et al., Chem. Phys. Lett. 499, 247 (2010).

23

Monday, May 30, 15.45–16.10 Leonhard Grill (20 + 5)

Study and Manipulationof Single Functional Molecules on Surfaces

Leonhard Grill

Fritz Haber Institute of the Max Planck Society, Dept. of Physical Chemistry, Faradayweg 4-6, 14195 Berlin

Molecules that exhibit a speciVc electronic, mechanical or optical function are of high interest as modelsystems for future applications in molecular nanotechnology where they should be used as single-moleculedevices. The scanning tunneling microscope (STM) is a suitable instrument to obtain fundamentalunderstanding of such molecules, because it can on the one hand image surfaces with atomic resolutionand is on the other hand capable to manipulate single atoms or molecules. In this talk, various examplesof manipulations of single functional molecules by low temperature STM will be given. The emphasis willbe on molecular switches, i.e. molecules that exhibit at least two stable states. For azobenzene derivativeson a metal surface, trans to cis isomerizations are obtained either by light or by STM manipulation. In thelatter case diUerent mechanisms, based on the tunneling electrons or the electric Veld in the junction, areidentiVed. By slightly modifying the chemical structure of the molecular switches, it is found that theatomic-scale environment of each individual molecule, i.e. the surrounding molecules and the surfaceunderneath, strongly inWuence the isomerization process and can either allow or suppress it. On theother hand, molecular switches that are based on an imine unit show evidence for an inverted thermalisomerization behavior as heating of the surface leads to a larger number of cis isomers, in contrast tothe known thermal cis to trans relaxation in solution. Moreover, the controlled assembly of functionalmolecules will be presented, whereas covalent bonding is the desired intermolecular interaction, becauseit provides high stability and the possibility of eXcient charge transfer.

CoUee break from 16.10 to 16.35.

24

Xiaoyang Zhu (30 + 5) Monday, May 30, 16.35–17.10

Exciton Fission and Dissociation at OrganicSemiconductor Interfaces

Wai-Lun Chan, Loren Kaake, Askat Jailaubekov, Manuel Ligges, X.-Y. Zhu

Department of Chemistry and Biochemistry, University of Texas, Austin, TX 78712, USA

Solar photovoltaics based on organic semiconductors commonly involve excitons. This results fromstrong Coulomb attraction between an electron and a hole due to the low dielectric constants of molecularmaterials. In this lecture, I will address the question of how excitons form, relax, multiple, and dissociate inorganic semiconductor materials and at their interfaces. We use time-resolved two-photon photoemissionspectroscopy (TR-2PPE) to track the electron in time and energy domains at it is initial excited, and as itrelaxes, multiplies, and transfers; this is complemented by time-resolved four wave mixing to monitor thetransient electric Veld formed from exciton dissociation and charge separation at the interface. One storyI will focus on is exciton Vssion or multiple exciton generation (MEG), which refers to the creation of twoor more electron-hole pairs from the absorption of a single photon. Using fullerene as electron acceptorand pentacene as MEG material where exciton Vssion occurs (singlet -> 2 triplets), we show the mosteXcient electron transfer not from the singlet or the triplets, but from an intermediate known as the darkmultiexciton (DME) quantum state. We directly observe the DME as it forms from the singlet, decays intotwo triplets, or transfers two electron to fullerenes to establish a transient interfacial electric Veld. Anexciting aspect of harvesting these excitons in dynamic time windows is that it may allow us to designsolar cells with eXciency exceeding the so-called Shockley-Queisser limit, which is the thermodynamiclimit of conventional solar cells.

25

Monday, May 30, 17.10–17.35 Christian Frischkorn (20 + 5)

Ferroelectric Ordering and Spin Polarizationof Thin Adsorbate Layers on Metal Surfaces

Christian Frischkorn1,2

1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany2Fachbereich Physik, Freie Universität Berlin, Germany

D2O–ice layers on a Ru(001) surface experiencing charge conVnement have been investigated usinginterface sensitive sum–frequency generation (SFG) spectroscopy. Irradiating the sample with 4.66 eVlight leads to electron transfer from the metal into the ice layer, where the vibrational response of thewater molecules in the OD stretch region is probed. Electron injection into crystalline layers enhances thesum–frequency signal up to a factor of more than 103 in the frequency region corresponding to vibrationsinvolved in hydrogen bonding, but does not inWuence the vibrations at the ice–vacuum interface. Theobserved changes do not spontaneously reverse back to the original state on a timescale of severalhours and strongly depend on the D2O structure, since no enhancement in the sum-frequency spectraof thin amorphous ice layers can be observed under otherwise identical experimental conditions. Ourproposed explanation for this phenomena involves partial ferroelectric ordering of the crystalline ice phaseexperiencing large electric Velds, which results in a net dipole moment of the D2O adsorbate throughmolecular reorientation. This causes symmetry breaking in the inner part of the ice layer which gives riseto the observed tremendous SFG signal enhancement [1].

The same vibrational spectroscopy method has been used also to investigate the coupling between aferromagnetic thin Vlm and adsorbed molecules thereon, in particular CO on Ni/Cu(100). It is found thatthe CO stretch vibration exhibits a signiVcant magnetic contrast with a steep temperature dependence.Despite a virtually zero net magnetic moment at the CO molecule, density functional theory calculationsindicate that the magnetic signal is caused by the partial spin moment per molecular orbital aligned alongthe magnetization direction. The temperature dependence can be related to atom and symmetry resolvedmagnetization densities which change when the CO stretch vibration is coupled to thermally excitedexternal modes like the frustrated translation and rotation [2].

[1] J. Bdžoch et. al., unpublished.

[2] H. Öström et. al., Phys. Rev. Lett. (submitted).

26

Peter Saalfrank (30 + 5) Monday, May 30, 17.35–18.10

Non-Adiabatic Molecular Dynamics at Metal SurfacesPeter Saalfrank, Gernot Füchsel, Tillmann Klamroth, Serge Monturet, Jean-Christophe

Tremblay, and Tijo Vazhappilly

Institute of Chemistry, University of Potsdam, D-14476 Potsdam, Germany

Non-adiabatic eUects, i.e., the coupling of nuclear and electronic motion and the breakdown of theBorn-Oppenheimer approximation, tend to be largely ignored in theoretical descriptions of moleculardynamics at solid surfaces. However, they are absolutely essential in various instances in particular whenmetal substrates are involved.

In the talk, I will focus on the theory of non-adiabatic dynamics at metal surfaces, on methods totreat them, and on examples which were recently studied in our group: (1) The vibrational relaxationof atomic and molecular adsorbates due to vibration-electron coupling – H/Pd(111) [1], H2/Ru(0001) [2],and NO/Au(111) [3]; (2) the control of the vibrational dynamics of relaxing adsorbates by shaped infraredlaser pulses – subsurface adsorption of H at Pd(111) driven by “laser distillation” [1]; (3) the vibrationalrelaxation of highly vibrationally excited NO molecules when scattering oU a Au(111) surface [3]; (4) thefemtosecond-laser induced, “hot electron” mediated associative photodesorption of H2 (D2) from Ru(0001)[2].

[1] J.C. Tremblay and P. Saalfrank, J. Chem. Phys. 131, 084716-1-17 (2009); J.C. Tremblay, S. Monturet,and P. Saalfrank, Phys. Rev. B 81, 125408-1-12 (2010).

[2] T. Vazhappilly, T. Klamroth, R. Hernandez, and P. Saalfrank, J. Phys. Chem. C 113, 7790-7801 (2009);G. Füchsel, T. Klamroth, J.C. Tremblay, and P. Saalfrank, Phys. Chem. Chem. Phys. 12, 14082-14094 (2010);G. Füchsel, T. Klamroth, S. Monturet, and P. Saalfrank, Phys. Chem. Chem. Phys., accepted.

[3] Serge Monturet and P. Saalfrank, Phys. Rev. B 82, 075404-1-10 (2010).

27

Monday, May 30, 18.10–18.45 Ulrich Höfer (30 + 5)

Ultrafast Electron Dynamics at Metal-/OrganicInterfaces

U. Höfer

Philipps-Universität Marburg, Fachbereich Physik und Zentrum für Materialwissenschaften, Renthof 5,35032 Marburg, Germany

Ultrafast surface spectroscopies, particularly time-resolved two-photon photoemission (2PPE), canprovide detailed information about the microscopic mechanisms of electron transfer processes at interfacesbetween organic molecular layers and metals. I will report about recent studies of 3,4,9,10-perylenetetracarboxylic acid dianhydride (PTCDA) and 1,4,5,8-naphthalene tetracarboxylic acid dianhydride(NTCDA) grown epitaxially on Ag(111). Both systems display an unoccupied dispersing state between themetallic Fermi level and the lowest unoccupied molecular orbitals. This state is shown to be a genuineinterface state. It has a strong overlap with the metal and plays an important role in the carrier transportacross the interface.

Work performed in collaboration with M. Marks, C. H. Schwalb, B. Schmidt, A. Namgalies (Marburg)and S. Sachs, A. Schöll, F. Reinert, and E. Umbach (Würzburg). Funded by the Deutsche Forschungsge-meinschaft through SPP1093, SPP1121, GK790, and GK1221.

Dinner at 19.00.Postersession II at 20.30.

28

Reinhard Kienberger (30 + 5) Tuesday, May 31, 8.30–9.05

Attosecond Spectroscopy on SolidsReinhard Kienberger

Technische Universität München, James Franck Str. 1, 85748 Garching, Germany

Atoms exposed to a few oscillation cycles of intense visible or near-infrared light are able to emit asingle electron and XUV photon wavepacket of sub-femtosecond duration [1,2]. Precise control of thesesub-femtosecond wavepackets have been achieved by full control of the electromagnetic Veld in few-cyclelight pulses [3]. These XUV pulses together with the few-cycle (few-femtosecond) laser pulses used fortheir generation have opened the way to the development of a technique for attosecond sampling ofelectrons ejected from atoms [4], molecules, and solids. This is accomplished by probing electron emissionwith the oscillating electric Veld of the few-cycle laser pulse following excitation of the atom by thesynchronized sub-femtosecond XUV pulse. Sampling the emission of photo electrons in this mannerallows time-resolved measurement of the XUV pulse duration as well as of the laser Veld oscillations[5]. After the full characterization of these tools, Vrst experiments have been carried out to measuresub-femtosecond behavior of matter. Recently, the dynamics of the photoionization process on solidshas been studied [6]. Not only that attosecond metrology now enables clocking on surface dynamics,but also the individual behaviour of electrons of diUerent type (core electrons vs. conduction bandelectrons) can be resolved. We measured a time delay of about 100 as on the emission of the aforementiontwo types of electrons in diUerent solid probes. We investigate electron transport in diUerent materialswith adlayers of varing thickness to gain information on transport eUects and other material properties.The information gained in these experiments may have inWuence on the development of many moderntechnologies including semiconductor and molecular electronics, optoelectronics, information processing,photovoltaics, electrochemical reactions, electronically stimulated chemistry on surfaces and interfaces,non-adiabatic reactions, optical nano-structuring, and interference eUects in spectroscopy.

[1] M. Hentschel et al., Nature 414, 501 (2001).

[2] R. Kienberger et al. Science 297, 1144 (2002).

[3] A. Baltuska et al., Nature 421, 611 (2003).

[4] R. Kienberger et al., Nature 427, 817 (2004).

[5] E. Goulielmakis et al. Science 305, 1267 (2004).

[6] A. Cavalieri et al., Nature 449, 1027 (2007).

29

Tuesday, May 31, 9.05–9.40 Anders Nilsson (30 + 5)

Ultrafast Studies of Bonding Rearrangements inAdsorbed CO on Ru Probed with LCLS

Anders R Nilsson1, Martina Dell’Angela2, Toyli Anniyev1, Martin Beye1,3, Ryan CoUee1,Alexander Föhlisch3, Jörgen Gladh4, Tetsuo Katayama1, Sarp Kaya1, Oleg Krupin1,

Dennis Nordlund1, Henrik Oström4, William F Schlotter1, Jonas A Sellberg1, FlorianSorgenfrei2, Joshua J Turner1, Martin Wolf5, Wilfried Wurth2

1SLAC National Accelerator Laboratory, California, United States2Institut fur Experimentalphysik, Universität Hamburg, Germany

3Helmholtz-Zentrum Berlin, Berlin, Germany4Department of Physics, Stockholm University, Stockholm, Schweden

5Fritz Haber Institute, Department of Physical Chemistry, Berlin, Germany

X-ray emission spectroscopy provides an atomic speciVc projection of the electronic structure allowingfor a detailed picture of chemical bonding on surfaces. There is a new opportunity to follow ultrafast elec-tronic structure changes during chemical reactions on surfaces with x-ray emission spectroscopy probedusing an x-ray laser. I will show recent experiments using LCLS to probe the laser induced desorption ofCO on Ru(0001) with 200 femtosecond resolution. During the transition from the chemisorbed, surfacebonded state to the free gas phase molecule, we observe considerable dynamics in the relevant occupiedand unoccupied pi-states and in the occupied sigma-states of CO.

30

Alfred Leitenstorfer (30 + 5) Tuesday, May 31, 9.40–10.15

Femtosecond Nanophotonics:Single Electrons, Photons and Sub-CycleConVnement of Light in Four Dimensions

Alfred LeitenstorferDepartment of Physics and Center for Applied Photonics,University of Konstanz, D-78457 Konstanz, Germany

At the beginning, ultrabroadband Er:Vber laser technology is introduced as an enabling tool for thework in femtosecond quantum photonics featured in the following [1]. Electronic excitations in low-dimensional semiconductor nanostructures readily sustain quantum coherence on a femtosecond timescale, even at room temperature. Aiming at applications in quantum metrology, we are developingprecise manipulation and readout of the quantum state of few-Fermion solid-state systems with the fastestpossible speed limited only by time-energ uncertainty.In a Vrst step, we have demonstrated deterministic excitation of a single electron-hole pair in a CdSe/ZnSequantum dot and direct analysis of the subsequent absorption changes with a broadband femtosecondprobe pulse. Working in a nonlinear readout regime, we are able to precisely change the number of photonsin a femtosecond laser pulse by ±1 [2]. We are now working our way towards tailoring the quantumstatistics of ultrashort pulses containing only a few quanta of light. To this end, the interaction betweensolid-state based few-level systems and broadband light Velds has to be further enhanced. One strategy isto couple single quantum dots to dielectric micropillar resonators with minimum intrinsic nonlinearity [3].Another concept relies on resonant plasmonic nanoantennas [4]. These systems exhibit very attractiveproperties like nonlinear emission of light out of spatial dimensions far below the wavelength scale andwith response times less than a single cycle of the fundamental plasmon resonance. Direct characterizationand engineering of such systems with nanometer and attosecond resolution will be presented [5].

[1] G. Krauss et al., Nature Photon. 4, 33 (2010).

[2] F. Sotier et al., Nature Phys. 5, 352 (2009).

[3] M. Kahl et al., Nano Lett. 7, 2897 (2007).

[4] J. Merlein et al., Nature Photon. 2, 230 (2008).

[5] T. Hanke et al., Phys. Rev. Lett. 103, 257404 (2009).

31

Tuesday, May 31, 10.15–10.40 Ralph Ernstorfer (20 + 5)

Lightwave-Control of Electronic Motionin the Solid State

A. SchiUrin1, T. Paasch-Colberg1,2, D. Gerster3, N. Karpowicz1, S. Mühlbrandt2,J. Reichert3, J.V. Barth3, R. Kienberger1,2, R. Ernstorfer5, and F. Krausz1,4

1Max Planck Institute of Quantum Optics, Garching2Technische Universität München, Department E113Technische Universität München, Department E20

4Ludwig-Maximilians-Universität, München5Fritz Haber Institute, Faradayweg 4-6, 14195 Berlin

The advent of intense few-cycle near infrared (NIR) laser pulses with stable and tunable carrier envelopephase (CEP) has enabled the control of electromagnetic Velds with attosecond time precision. Here we aimat exploiting these few-cycle NIR optical Velds with well-deVned CEP to generate and control the motionof charge carriers within nano-scaled solid state heterostructures. Applying such laser pulses to unbiasedmetal-dielectric-metal nano-gaps, we demonstrate the generation of directly measurable photocurrentswhose magnitude and directionality can be controlled with the laser CEP. This eUect vanishes with theincrease of the laser pulse duration. We interpret these phenomena as the signature of Veld-inducedgeneration of free carriers in the dielectric with subsequent directional acceleration of the carrier in theultrashort laser Veld. This ultrafast current injection at a nanoscaled condensed matter system representsa Vrst step towards the realization of light-Veld controlled electronics.

CoUee break from 10.40 to 11.05.

32

Lukasz Piatkowski (20 + 5) Tuesday, May 31, 11.05–11.30

Ultrafast Dynamics of Interfacial Water Revealed by2-Dimensional Surface Vibrational Spectroscopy

Lukasz Piatkowski, Zhen Zhang, Huib J. Bakker and Mischa Bonn

FOM-Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.

At the surface or interface of water, the water hydrogen-bonded network is abruptly interrupted,conferring properties on interfacial water diUerent from bulk water. Despite its importance for disciplinessuch as electrochemistry, atmospheric chemistry and membrane biophysics, the structure of interfacialwater has remained highly debated. We elucidate the structure and structural dynamics of interfacialwater using ultrafast two-dimensional surface-speciVc vibrational spectroscopy [1]. We present data forthe water-air and water-lipid interfaces, which reveal interfaces that are structurally heterogeneous, yethighly dynamical. We determine the timescale on which the heterogeneity decays and reveal the presenceof surprisingly rapid inter- and intramolecular energy transfer processes.

[1] J. Bredenbeck, A. Ghosh, H.K. Nienhuys, and M. Bonn, Acc. Chem. Res. 42 1332, (2009).

Young investigator session from 11.30 to 12.45.Lunch at 12.45.Excursion at 14.00.Conference dinner at 19.00.

33

Tuesday, May 31, 20.30–21.05 Margaret Murnane (30 + 5)

Bright Coherent Attosecond Kiloelectronvolt X-raySupercontinua and Applications in Nanoscience and

NanotechnologyT. Popmintchev, S. Mathias, M.M. Murnane, Andrius Baltuška*, H.C. Kapteyn

JILA, University of Colorado, Boulder, Colorado 80309, USA*Photonic Institute, Vienna University of Technology, Austria

We demonstrate bright coherent high harmonic (HHG) X-rays at photon energies >1.6 keV (<7.8 Å),promising to realize a coherent ultrafast implementation of the Roentgen X-ray tube in a tabletop-scaleapparatus [1-3]. Full phase matching of HHG in the keV region of the spectrum (>5031th order) is possiblefor the Vrst time by using driving laser wavelengths around 3.9 µm. We also generate the broadest coherentsupercontinuum to date of >1.3 keV, from any light source, large or small scale. This ultrabroad bandwidthcan support unprecedented single-digit attosecond pulse durations – 2.5 as – scalable to zeptosecond timescales (1 zs = 10−21 s).

Applications of high harmonic soft x-rays in materials and molecular science at surfaces will also bediscussed, including capturing element-speciVc ultrafast demagnetization dynamics with ≈ 10 fs temporalresolution, implementing coherent diUractive (lensless) imaging with 22 nm spatial resolution, and infollowing energy Wow in nanostructures.

A. Predicted HHG full phase matching cutoUs as a function of the driving laser wavelength, wherebright HHG emission is possible. Solid circles represent current experimental results and open circles– theoretically expected phase matching limits. The absence of inner shell absorption in He allowsfor generation of bright keV X-rays. B. Fully phase matched X-ray supercontinuum up to >1.6 keV or7.8 Å (note linear X-ray intensity scale) with bandwidth >1.3 keV (tail to tail). C. Transform limited2.5 attosecond pulse duration supported by the supercontinuum in B, together with spatial proVle of thecoherent X-ray beam.

[1] T. Popmintchev et al., Postdeadline paper, CLEO Conference, May 2011.

[2] M.C. Chen et al., Phys. Rev. Lett. 105, 173901 (2010).

[3] T. Popmintchev et al., Nature Photonics 4, 822-832 (2010).

34

Pedro Echenique (30 + 5) Tuesday, May 31. 21.05–21.40

Electron Dynamics at Surfaces and NanostructuresP. M. Echenique

Dpto. de Física de Materiales UPV-EHU, Donostia International Physics Center (DIPC) and MaterialPhysics Center (CFM), P. Manuel de Lardizabal 4, 20018 San Sebastián, Basque Country, Spain

Femtosecond and subfemtosecond time scales typically rule electron dynamics at metal surfaces. Recentadvances in experimental techniques allow the experimental study of such dynamics. In this talk weshall analyze electron dynamics at surfaces and nanostructures with emphasis on screening times, spindependence of charge transfer of adsorbates and smaller system sizes. Condensed matter eUects onattophysics will also be discussed.

Drinks and discussion afterwards.

35

Wednesday, June 1, 8.30–9.05 Martin Aeschlimann (30 + 5)

Ultrafast Optical Control of Magnetism at the NanoscaleMartin Aeschlimann

Department of Physics and Research Center OPTIMAS, TU Kaiserslautern, Germany

I will present results in the newly-emerging multidisciplinary Veld of “all optical magnetizationreversal”, a new scientiVc area with novel technological opportunities at the junction of coherent controlschemes and magnetism. Since the Rasing group in Nijmegen has demonstrated in 2007 that an ultrashortcircularly polarized laser pulse acts on spins as a similarly short magnetic Veld pulse with strengths up to1 T, the question arises about the responsible microscopic mechanism for this astonishing eUect. Althoughpreviously believed to be impossible, even the reversal of magnetization by a single 40 femtosecondcircularly polarized laser pulse was achieved without any applied magnetic Veld. The direction of thisopto-magnetic switching was unambiguously set by the helicity of light. To gain a deeper understandingof the underlying microscopic mechanisms, especially regarding the role of the spin-orbit-coupling,we investigated the optimal parameters of the laser pulse (power, wavelength, duration, spectra, chirp,temporal proVle) that provides the most eUective laser control of magnetism in rare earth/transition metalalloys. In particular, the storage of helicity information after decoherence between electrons and the lightVeld is an open question, as the helicity-dependent magnetization reversal takes much longer than the laserpulse duration. Another open question we studied is the optimal (and technologically most interesting)material system for all-optical reversal. Until now all-optical switching is only realized and observedin ferromagnetic rare earth/transition metal alloys with an out of plane anisotropy. In this context thelocalized 4f-levels of the rare earth component are a possible candidate as a long-lived reservoir for thehelicity information. The review concludes with a summary and an outlook to the feasibility of lasercontrol of magnetism at the nanoscale.

36

Tobias Kampfrath (20 + 5) Wednesday, June 1, 9.05–9.30

Nonlinear Terahertz Spectroscopyof Magnetically Ordered Solids

Tobias Kampfrath

Fritz Haber Institute of the Max Planck Society, Berlin, Germany

Terahertz (THz) spectroscopy is nowadays routinely used to investigate the electron dynamics in manyphysical systems. Up to now, a minor part of THz work has focused on magnetically ordered systems.Moreover, the interaction between the THz pulse and the sample has been mediated by the electric ratherthan the magnetic Veld of the THz wave. Here, we report on two examples demonstrating that THzspectroscopy is a powerful tool to study the orbital and spin dynamics of electrons in magnetically orderedsolids. First, we show that the THz pulse emitted from a photo-excited ferromagnetic Fe Vlm is highlysensitive to the motion of spin-polarized electrons along the Vlm interfaces. Second, the magnetic Veldof an intense THz pulses is used to switch on and oU a magnon in the antiferromagnet NiO via Zeemancoupling to the NiO spins [1].

[1] T. Kampfrath, A. Sell, G. Klatt, A. Pashkin, S. Mährlein, T. Dekorsy, M. Wolf, M. Fiebig, A. Leitenstorfer,and R. Huber, Nature Phot. 5, 31 (2011).

37

Wednesday, June 1, 9.30–9.55 Alexey Melnikov (20 + 5)

Experimental Approach for Investigation of SpinDynamics Excited by Femtosecond Pulses of

Spin-Polarized Hot CarriersA. Melnikov1,2, I. Razdolski3, T.O. Wehling4, E.Th. Papaioannou2, V. Roddatis5,

P. Fumagalli2, O. Aktsipetrov3, A.I. Lichtenstein4, U. Bovensiepen2,6

1Physical Chemistry Department, Fritz-Haber-Institute of the Max Planck Society, Faradayweg 4-6, 14195Berlin, Germany

2Phys. Dept., Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany3Physics Department, Moscow State University, 119991 Moscow, Russia

4Theoretical Physics Institute, University of Hamburg, Jungiusstr. 9, 20355 Hamburg, Germany5NRC "Kurchatov Institute", pl. Ak. Kurchatova 1, Moscow, 123182, Russia

6Faculty of Phys., Univ. Duisburg-Essen, Lotharstr. 1, 47048 Duisburg, Germany

Magnetization dynamics induced by a transport of spin polarized carriers is a hot topic due to thefundamental interest in spin excitations, their coupling to electron and lattice sub-systems and applicationsin spintronics and data storage. However, experiments usually performed in electrical circuits experience alack of femtosecond time resolution. The ultrafast magnetization dynamics induced by femtosecond laserpulses is studied extensively but the understanding of underlying elementary processes is embarrassed bythe limited ability of conventional pump-probe schemes to distinguish photon-, electron-, and phonon-mediated eUects.

In our experiments we demonstrate a pump-probe study of spin polarized hot carrier (HC) transportthrough an epitaxial Au/Fe/MgO(001) structure. Following a time-of-Wight like approach, which we realizein a back-pump-front-probe conVguration, we establish that HC induced in Fe by the pump laser pulseand injected from Fe into Au can form a nearly ballistic spin current. Optical second harmonic (SH)generated at the Au surface by the probe pulse monitors the transient surface spin polarization induced byHC. We show that the diUusive or ballistic character of HC transport is set by the spin polarization of thepropagating HC, which we explain by the smaller electron-electron scattering rate of the minority HC inAu.

Besides that, SH monitoring of the Fe/MgO interface with the pump pulse applied from either Fe or Auside of the structure allows us to compare the ultrafast magnetization dynamics excited in Fe either bydirect optical pumping or by HC generated in Au since the Au thickness is larger than the light penetrationdepth. This comparison performed for diUerent thicknesses of Fe Vlms sheds light to the role of HC in theultrafast demagnetization of ferromagnetic metals.

CoUee break from 9.55 to 10.20.

38

Uwe Bovensiepen (30 + 5) Wednesday, June 1, 10.20–10.55

Decay of Hot Quasi-Particlesin Two-Dimensional Materials

Uwe Bovensiepen

University Duisburg-Essen, Faculty of Physics, Lotharstr. 1, 47048 Duisburg, Germany

Electron dynamics in solid systems proceed on femto- and attosecond timescales and comprise mo-mentum and energy dependent processes. Femtosecond time- and angle-resolved photoemission usingultrashort laser pulses is well established for the analysis of excited states and their relaxation. In thistalk two topical examples, where time-resolved photoelectron spectroscopy was used to study ultrafastelectron dynamics in two-dimensional systems, will be presented. (i) In epitaxially grown metallic Pblayers on Si(111) of 1 to 20 monolayer thickness we Vnd for Pb electrons at energies within the substrateband gap a quantitative agreement of the hot electron lifetime with Fermi liquid theory. We attributedeviations at higher energies degenerate with the Si conduction band to electron transfer processes. (ii)In the layered high-𝑇𝑐 superconductor BSCCO we observe for optimal doping a momentum dependentquasi-particle population which reWects metastable quasi particles in the vicinity of the anti-node of thed-wave gap function. Their decay through Cooper pair formation will be discussed.

39

Wednesday, June 1, 10.55–11.30 Hrvoje Petek (30 + 5)

Exploring the Electronic Structure and Dynamics in theInner Space of 0D-2D Hollow Molecules

by STM, 2PP, and TheoryHrvoje Petek

Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260

Hollow molecules formed by rolling and wrapping molecular sheets into nanotubes and fullerenes arefascinating objects because of their novel electronic structures as well as atomic and molecular inclusionsthey may contain within them. In addition to electronic wavefunctions that are centered on atoms, hollowmolecules also posses atom-like superatom states with electronic wavefunctions bound to the hollowcores.[1,2] These superatom states are derived from the image potential states of the parent molecularsheet, speciVcally graphene in the case of carbon nanotubes and fullerenes.[3] The property of superatomstates to form nearly-free electron bands through nonnuclear density maxima of hollow cores make theminteresting for charge transport; therefore, we explore conditions which stabilize the superatom states tothe conduction band minimum.[4] We further explore the electronic structure and dynamics of fullereneswith atomic and molecular inclusions.[5] The superatom states interact with the included species suchthat their charge transfer excitation can trigger internal isomerization. We explore the internal surfacefemtochemistry as a model for single molecule machines. [1] Feng, M.; Zhao, J.; Petek, H.: Atomlike,

Hollow-Core-Bound Molecular Orbitals of C60. Science 2008, 320, 359-362.

[2] Feng, M.; Zhao, J.; Zhu, X. Y.; Petek, H.: The electronic properties of superatom states of hollowmolecules. Acc. Chem. Res. in press.

[3] Silkin, V. M.; Zhao, J.; Guinea, F.; Chulkov, E. V.; Echenique, P. M.; Petek, H.: Image potential states ingraphene. Phys. Rev. B 2009, 80, 121408-4.

[4] Hu, S.; Zhao, J.; Jin, Y.; Yang, J.; Petek, H.; Hou, J. G.: Nearly Free Electron Superatom States of Carbonand Boron Nitride Nanotubes. Nano Letters 2010, 10, 4830-4838.

[5] Huang, T.; Zhao, J.; Feng, M.; Petek, H.; Yang, S.; Dunsch, L.: Superatom orbitals of Sc3N@C80 andtheir intermolecular hybridization on Cu(110)-(2x1)-O surface. Phys. Rev. B 2010, 81, 085434.

40

Tobias Hertel (30 + 5) Wednesday, June 1, 11.30–12.05

Radiative and Non-Radiative Decay in CarbonNanotubes

Tobias Hertel

Institute of Physical and Theoretical Chemistry, Julius-Maximilians University Würzburg, Germany

We will discuss the current understanding and recently gained insights into radiative and non-radiativeprocesses in metallic and semiconducting single-wall carbon nanotubes (SWNTs). SpeciVcally, we willfocus on the determination of exciton photoabsorption cross sections, oscillator strengths, size, mobilityand non-radiative decay mechanisms [1,2]. We will also brieWy discuss the ongoing development ofnanosurface spectroscopy, a broader eUort of our group to develop experimental tools and methods for theinvestigation of kinetics and dynamics of chemical change at nanoparticle-solvent interfaces.

[1] T. Hertel, S. Himmelein, T. Ackermann, D. Stich, J. Crochet, ACS Nano. 4, 7161 (2010).

[2] L. Luer, S. Hoseinkhani, D. Polli, J. Crochet, T. Hertel, G. Lanzani, Nature Phys. 5, 54 (2009).

41

Wednesday, June 1, 12.05–12.40 Tony F. Heinz (30 + 5)

Seeing Electrons in Two Dimensions:Optical Spectroscopy of Graphene

K. F. Mak1, C. H. Lui1, L. M. Malard1, Z. Q. Li1, D. Boschetto1,2, M. Sfeir3, J. A.Misewich3, J. Shan4, T. F. Heinz1

1Columbia University, New York, NY 10027, USA2Laboratoire d’Optique Appliquée, ENSTA/Ecole Polytechnique, Palaiseau, France

3Brookhaven National Laboratory, Upton, NY 11973 USA4Case Western Reserve University, Cleveland, OH 44106, USA

Optical spectroscopy complements transport measurements as a means of understanding the distinctiveproperties of electrons graphene. Within the simplest description, one has for graphene a zero-gapsemiconductor with direct transitions between the conical bands. This gives rise to a predicted absorptionthat is frequency independent and has a strength of 𝜋𝛼= 2.3%, where 𝛼 is the Vne-structure constant.This result is indeed obtained experimentally in the near infrared [1], but at higher photon energiesband-structure eUects and electron-hole interactions signiVcantly modify this behavior [2].

Optical absorption spectroscopy also permits probing of how the linear bands of graphene are modiVedthrough interlayer interactions. In particular, graphene bilayers support a band gap under the application aperpendicular electric Veld. Such a tunable band gap, with a magnitude up to 200 meV, has been observedby infrared measurements [3]. For the case of few-layer graphene samples, more complex 2D bandstructure develops, as reWected in optical absorption spectra [4].

Another important aspect of laser spectroscopy is the ability to examine the underlying dynamics bytime-resolved techniques. We describe characterization of the femtosecond electron dynamics using lightemission from graphene induced by femtosecond laser pulses [5]. The studies reveal very rapid electronthermalization, as well as equilibration with strongly coupled optical phonons.

[1] K. F. Mak, M. Y. Sfeir, Y. Wu, C. H. Lui, J. A. Misewich, and T. F. Heinz, Phys. Rev. Lett. 101, 196405(2008).

[2] K. F. Mak, J. Shan, and T. F. Heinz, Phys. Rev. Lett. 106, 046401 (2011).

[3] K. F. Mak, C. H. Lui, J. Shan, and T. F. Heinz, Phys. Rev. Lett. 102, 256405 (2009).

[4] K. F. Mak, M. Sfeir, J. A. Misewich, T. F. Heinz, Proc. Nat. Acad. Sci. 107, 14999 (2010).

[5] C. H. Lui, K. F. Mak, J. Shan, and T. F. Heinz, Phys. Rev. Lett. 105, 127404 (2010).

Lunch at 12.45.

42

Poster Abstracts

Poster sessions will take place on Sunday and Monday evening starting at 8.30pm.

Poster presenters who take part in the competition for the young investigator session are indicated by"YIS" on their abstract and are asked to attach a respective sign to their poster. The YIS committee willdecide on the three speakers based on the poster session I on Sunday evening.

P1 YIS Martin Beye

The Two Steps in the Ultrafast Melting of SiliconObserved by Snapshots of Valence Electrons

Martin Beye1, Florian Sorgenfrei2, William F. Schlotter3, Wilfried Wurth2, AlexanderFöhlisch1

1Helmholtz-Zentrum Berlin, Institut für Methoden und Instrumentierung der Synchrotronstrahlung2Universität Hamburg, Institut für Experimentalphysik und Centre for Free-Electron Laser Science

3SLAC National Accelerator Laboratory

Microscopic models for the “anomalies of water” are still lacking an experimental proof, althoughanomalous thermodynamic behaviour is common for a class of matter that forms tetrahedral networks -like water, diamond or silicon. Their phase diagrams are very rich, but the exploration of large areas hasbeen limited mostly to theoretical studies. And yet, remainders of those experimentally unaccessible areascontribute to the properties at standard conditions. For example a possible explanation for the anomalies isbased on the existence of a liquid-liquid phase transition in the supercooled region. With the combinationof ultrashort optical laser pulses and soft X-ray pulses from FLASH, the free-electron laser in Hamburg,we study the melting dynamics of silicon in detail. We Vnd two distinct melting steps separated by severalpicoseconds, which we attribute to the disputed liquid-liquid phase transition. With this study we exploitthe novel possibilities at X-ray free-electron lasers. These machines allow for adding femtosecond timeresolution to the highly selective information gained about the full electronic structure with soft X-rayspectroscopic methods. [1]

[1] M. Beye, F. Sorgenfrei, William F. Schlotter, W. Wurth, A. Föhlisch, Proc. Natl. Acad. Sci. USA 107,16772 (2010).

44

Daniele Brida P2 YIS

Ultrafast Electron Dynamics in GoldDaniele Brida, Giulio Cerullo

IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy.

The energy relaxation dynamics of a Fermi liquid are important to understand the physical properties ofsolids, with both fundamental and applied relevance. In particular electron-electron interaction (EEI) andelectron-phonon interaction (EPI) mechanisms are crucial in determining electrical and thermal properties.The early steps of such processes occur on the 100-fs timescale, thus challenging the temporal resolution ofcurrently available spectroscopy systems. In this study we perform two-colour pump-probe experimentson Gold Vlms with a unique combination of high temporal resolution and broadband detection, whichenables mapping the equilibration dynamics of the electron distribution with unprecedented detail.

Gold is a among the metals with the lowest EPI and is particularly suited to study the thermalizationdynamics that takes place when an out-of equilibrium electron distribution is created in the conductionband by an impulsive optical excitation. The band structure of gold, in fact, shows a d-band well localizedat 2.2 eV below the Fermi Level, and a visible pulse can probe the joint density of states (DOS) around theFermi level as perturbed by an impulsive excitation of conduction band electrons. By using an ultrashortpump pulse a non-thermal electron distribution is created, which then rapidly evolves to a thermaldistribution via EEI; subsequently the electrons thermalize with the lattice via EPI. The large DOS of thed-band electrons ensures that the transient signal measured in a pump-probe experiment is dominated byd-band to conduction band transitions [1].

By tuning the ultrashort (sub-10 fs) pump pulse energy to the infrared [2], one excites electrons atlower energies so that the electron distribution covers a narrower energy spectrum in the conduction bandwith respect to the pulse shifted to the blue. In particular we could observe that the pump-probe signalin the thermal distribution around 2.2 eV displays a faster rise-time for a blue-shifted pump. This is aconsequence of the fact that electrons with higher excitation energy above the Fermi level possess a fasterscattering rate, as predicted by the Fermi Liquid Theory. This theory, however, seems is not suXcient tofully describe the observed signals.

[1] C.-K. Sun et al. Phys. Rev. B 50, 15337-15348 (1994).

[2] D. Brida et al., J. Opt. 12, 013001 (2010).

45

P3 YIS Christopher Bronner

Electronic Structure of Bottom-Up FabricatedGraphene Nanoribbons at the Gold SurfaceChristopher Bronner, Felix Leyssner, Stephan Meyer, Petra Tegeder

Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany

Besides single-layered graphene sheets and carbon nanotubes, a third branch of interesting carbonmaterials is currently in the focus of research. Graphene nanoribbons show properties attractive for theuse in nanoscale electronic devices as the band structure of these quasi-one-dimensional structures istunable by variation of the ribbon width on the order of nanometers. Particularly the size of the band gapis of great interest as its variation allows to choose between metallic and semiconducting nanoribbonswhich could be employed as molecular wires or Veld-eUect transistors, respectively.We present combined two-photon photoemission (2PPE) and high resolution electron energy loss spec-troscopy (HREELS) investigations of bottom-up fabricated graphene nanoribbons with N=7 carbon atomswidth on a Au(111) surface. The HOMO-LUMO gap was determined and three unoccupied electronicstates are found. In order to elucidate these states’ nature, their dispersion along the ribbon axis and theirultrafast electron dynamics was measured in angle- and time-resolved 2PPE measurements.

46

Robert Carley, Björn Frietsch P4 YIS

Femtosecond XUV Photoelectron Spectroscopy ofUltrafast Magnetization Dynamics in Gadolinium and

TerbiumRobert Carley1, Björn Frietsch1, Kristian Döbrich1, Martin Teichmann1, Cornelius

Gahl1, Frank Noack1, Olaf Schwarzkopf2, Philippe Wernet2, Martin Weinelt1,3

1Max-Born-Institut, Berlin2Helmholtz-Zentrum für Materialien und Energie (BESSY II), Berlin

3Fachbereich Physik, Freie Universität, Berlin

The Lanthanide metals Gadolium and Terbium are prototypical local-moment ferromagnets, in whichthe magnetic moment derives predominantly from the partial occupancy of the localized 4𝑓 core electroniclevels. Alignment of the magnetic moments between adjacent atoms in the lattice occurs by spinpolarization of the itinerant 5𝑑 and 6𝑠 valence electrons in an indirect exchange (RKKY) interaction.

Recent work using ultrafast laser pulses to demagnetize these materials [1,2] has revealed that thedemagnetization proceeds on an ultrafast timescale. Presented here are results of our time-resolvedIR-pump-XUV-probe angle-resolved photoelectron spectroscopy (TR-ARPES) experiments on the ultrafastdemagnetization of thin Vlms Gd (0001) and Tb (0001) on W (110), which add signiVcant insights in thisVeld. The experiments are the Vrst to be done using a newly developed high-order harmonics (HHG) XUVsource and beamline, which delivers monochromated XUV pulses of approximately 150 fs duration withan energy resolution of up to 150 meV, at a Wux of 1× 105 photon/pulse at a repetition rate of 10 kHz.

Following excitation by an intense infrared (IR) pulse of 200 - 300 fs duration, TR-ARPES with XUVphotons of around 35 eV energy allows us to directly probe all the key electronic states involved inmagnetization, namely the 4𝑓 core levels, the valence band, and the occupied surface state, and thusobserve the magnetization dynamics. As signatures of ultrafast demagnetization of the metal by the IRpulse, we see for example, a rapid strong reduction of the exchange splitting in the valence band of bothmetals. This is followed by a slower further demagnetization due to the spin-lattice interaction.

[1] A. Melnikov et al, Phys. Rev. Lett. 100, 107202 (2008)

[2] M. Wietstruk et al, Phys. Rev. Lett. (2011) in press

47

P5 YIS Jan-Christoph Deinert

A 2PPE-Study of Pyridine/ZnO(1010):From the Characterization of the Setup

to First Time-Resolved SpectraJan-Christoph Deinert, Sebastian Hagen, Julia Stähler, Martin Wolf

Abteilung Physikalische Chemie, Fritz-Haber-Institut der Max-Planck Gesellschaft, Berlin, Deutschland

The features and functionality of an optoelectronic device, such as an OLED, are mainly basedon the electronic band structure of its constituents. Hybrid systems built of organic molecules ona metallic or semiconducting substrate may allow for tailoring of the electronic structure and thusenable the optimization of this functionality. However, thorough low-level understanding of evensimple hybrid systems, i. e. comparably small molecules on a well-deVned substrate, as in the case ofpyridine/ZnO(1010), has not been established so far.

In my contribution, I describe the Vrst stages and results of a femtosecond two-photon photoemission(2PPE) experiment that is designed for the examination of the surface and interface electronic bandstruc-ture of such hybrid systems. The method of 2PPE enables us to study the structure of occupied andunoccupied electronic states, which gives us access to the functional core of the optoelectronic mechanism.Our setup, which was built from scratch, comprises a PHOIBOS 100 hemispherical electron analyser whichallows for the simultaneous measurement of both energy and angular distribution, i. e. dispersion relation𝐸(k), of the nascent photoelectrons. The latter feature gives direct experimental access to the degree oflocalization of the electrons, which may undergo changes due to reorganization eUects of the moleculesafter photoexitation. However, the precise measurement of the dispersion is highly sensitive to electricalVelds between sample surface and the analyser. These diXculties are tackled by appropriate bias voltagesand a custom-designed µ-metal nozzle that ensures Veld-free passage of the photoelectrons to the lenssystem of the analyser.

Despite these challenging complexities in the setup, Vrst 2PPE-measurements of the electronic structureof the model hybrid system pyridine/ZnO(1010) are shown. For approximately monolayer coverage ofpyridine we Vnd a spectral signature that can be attributed to a usually unoccupied interface state at about1.7 eV above 𝐸F, which is in agreement with preliminary DFT calculations of the pyridine/ZnO(1010)interface. For mutilayer coverages, only the electronic structure of the pyridine is probed due to the highlysurface sensitive 2PPE-method. Here we see an initially occupied molecular state about 0.9 eV below𝐸F, which may be attributed to the HOMO of the pyridine. Furthermore, Vrst picosecond-time-resolvedexperiments of this organic-inorganic hybrid system will be presented and discussed.

48

Cornelius Gahl P6

Charge and Energy Transfer Dynamics inSelf-Assembled Monolayers of Azobenzene-Derivatives

Cornelius Gahl1,2, Roland Schmidt1,2, Robert Carley1, Daniel Brete1,2, Stefanie Wagner1,Wolfgang Freyer1, and Martin Weinelt1,2

1Max-Born-Institut, Max-Born-Str. 2a, 12489 Berlin2Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin

Self-assembled monolayers (SAMs) are considered as a versatile platform for functionalization ofsurfaces. Building such SAMs from molecules containing photochromic moieties denotes a challengebecause the interaction of the molecular switch with its surrounding in most cases inhibits photo-isomerization.

For azobenzene alkanethiolate SAMs on gold, we investigated by resonant core-level spectroscopythe time-scale of charge transfer between chromophore and metal substrate for diUerent spacer chainlengths. While for 3 methyl units the excited electron can tunnel to the substrate within ∼100 fs, itslifetime exceeds the time-scale accessible by the experimental method for 6 and 10 methyl units. Thus thechromophore is strongly decoupled from the substrate already by relatively short alkyl chains.

Besides the vertical coupling to the substrate, lateral interaction among the azobenzene moieties hasto be considered due to the high packing density of the SAM. As evidenced by a strong blue shift ofthe absorption spectrum, optical excitation stays no longer localized at a single chromophore but isdistributed within the layer by excitonic coupling. From the exciton band width we estimate a time-scaleof few femtoseconds, much faster than the photo-isomerization process. These results demonstratethat intermolecular energy transfer can play an important role for the functionality of self-assembledmonolayers.

49

P7 YIS Kerstin HanU

Time- and Angle-Resolved Photoelectron Spectroscopyof Rb Intercalated 1𝑇–TaS2

Kerstin HanU, Stefan Hellmann, Timm Rohwer, Christian Sohrt, Michael Bauer, LutzKipp, and Kai Rossnagel

Institute of Experimental and Applied Physics, University of Kiel, Germany

Ultra-short high-harmonic pulses enable us to study ultrafast dynamics of condensed matter systemson femto- and picosecond time scales. In particular, they allow us to identify the nature and strength ofinteractions between various degrees of freedom in complex materials, in which typically two or more ofthe lattice, charge, spin and orbital degrees of freedom are strongly coupled. Layered transition-metaldichalcogenides (TMDCs) provide a variety of lattice and charge ordering phenomena such as charge-density waves (CDWs) and Mott insulating states. Our recent studies focused on the investigation ofelectronically driven CDWs employing time- and angle-resolved photoelectron spectroscopy [1,2].

Here, we present the ultrafast dynamics of a lattice driven CDW system. Rb adsorption on 1𝑇–TaS2serves as a model system revealing a pronounced metal-to-insulator transition. Induced by a chargetransfer, this intercalation process leads to a structural change into a commensurate CDW phase [3,4].Upon photoexcitation by an optical pump pulse the electronic gap closes and the Peierls insulator Rb:TaS2undergoes a transition into a transient metallic state. We are able to distinguish diUerent time scalesduring the excitation and relaxation processes, which indicate the inWuence of the electronic and latticesystems.

[1] T. Rohwer et al., Nature 471, 490-493 (2011).

[2] S. Hellmann et al., Phys. Rev. Lett. 105, 187401 (2010).

[3] K. Rossnagel et al., Phys. Rev. Lett. 95, 126403 (2005).

[4] K. Rossnagel, New Journal of Physics 12, 125018 (2010).

50

Tian Huang P8

Electron Stimulated Dynamics of the EncapsulatedCluster in an Endohedral Fullerene

Tian Huang1, Jin Zhao1, Min Feng1, Alexey A. Popov2, Shangfeng Yang2,3, LotharDunsch2, Hrvoje Petek1

1Department of Physics and Astronomy and Petersen Institute of NanoScience and Engineering, Universityof Pittsburgh, Pittsburgh PA 15260 USA

2Department of Electrochemistry and Conducting Polymers, Leibniz-Institute for Solid State and MaterialsResearch (IFW), Dresden, Germany

3Hefei National Laboratory for Physical Sciences at Microscale and Department of Materials Science andEngineering, University of Science and Technology of China (USTC), Hefei 230026, China

The tunneling electrons from a scanning tunneling microscope were used to induce the rotationalmotion of the encapsulated 𝑆𝑐3𝑁 cluster of a 𝑆𝑐3𝑁@𝐶80 molecule adsorbed on the Cu(110)-O surface at4.7 K. Experimental results and DFT calculations reveal that the 𝑆𝑐3𝑁 cluster has two types of motions,i.e., the in-plane rotation around a perpendicular 𝐶3 axis of the 𝐶80 cage and the axis switching out-of-plane rotation, under the excitation of tunneling electrons. Analysis of 𝐼 − 𝑡 series of diUerent switchingevents indicates the co-existence of both vibrational and electronic excitation mechanisms. The motions ofthe 𝑆𝑐3𝑁 cluster result in the controllable hierarchical switching behavior of the 𝑆𝑐3𝑁@𝐶80 molecule,making 𝑆𝑐3𝑁@𝐶80 an unique molecular switch with well protected moving parts.

51

P9 YIS Harald Kirsch

Photoinduced Formation of Atomic Oxygenand CO Oxidation on Thin MgO/Ag(001) Films

Harald Kirsch, Philipp Giese, C. Frischkorn, M. Wolf

Fritz-Haber-Institut, Abt. Physikalische Chemie, Faradayweg 4-6, 14195 Berlin

The photoinduced reduction of N2O has been studied on thin MgO Vlms grown on Ag(100) withtemperature programmed desorption (TPD) spectroscopy. After irradiation with a KrF laser (248 nm),an increasing N2 signal is observed together with a decrease of the parent N2O mass. In addition,recombinative desorption of oxygen appears at about 550 K. After several cycles of UV induced N2Oreduction, however, without subsequent heating over 300 K, the observed N2 formation is dramaticallyreduced. Analysis of the reaction yield as a function of the photon dose provides quantitative values of thecross sections for the N2O reduction reaction. The proposed reaction mechanism involves electron-holepairs created by the UV photons at edges of the MgO Vlm. These charges then get trapped at defect sitesand are responsible for the dissociation process of the N2O species [1]. The observed reduction in theN2 signal, when the sample is not restored at suXciently high temperatures, is interpreted by blockingof these reactive sites via occupation with atomic oxygen. In addition, as a prototype system for thechemistry with atomic oxygen, the CO oxidation has been studied with TPD as a function of photonexposure. If the coadsorbate is irradiated with UV light, a CO2 desorption peak at about 300K appears,accompanied by a depletion of the oxygen.

[1] O. Diwald, J. Chem. Phys. 116, 1707 (2002)

52

Michael Krüger P10 YIS

Strong-Field EUects and Attosecond Control ofElectrons in Photoemission from a Nanoscale Metal Tip

Michael Krüger, Markus Schenk, Peter HommelhoU

Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, D-85748 Garching, Germany

A sharp metal tip irradiated by femtosecond laser pulses represents an ultrafast laser-driven nanoscaleemitter of electrons. In our experiment we focus low-power Ti:sa oscillator pulses tightly on the apexof tungsten tip and measure photoelectron spectra. We observe above-threshold photoemission with aphoton order of up to nine, and, at intensities exceeding 1011 W/cm

2, we observe the suppression of thelowest-order peak as well as a shift of the spectral features towards lower energies [1]. This shift scaleslinearly with intensity with a slope of −1 eV/1012 W/cm

2. We conclude that these phenomena owe tothe AC Stark shift of the continuum states and are thus strong-Veld eUects. We Vnd that the laser electricVeld at the tip’s apex is enhanced by a factor of about 4, enabling us to enter the strong-Veld regime withlow-power oscillator pulses only. Moreover, we observe a plateau in the high-energy part of the spectra.In analogy to gas phase experiments, the plateau indicates that a fraction of liberated electrons undergoeselastic recollision with the metal surface.

Furthermore, we report on strong carrier-envelope phase (CEP) eUects in the electron spectra, withalmost full current modulation at high energies [2]. We model the results with the extended simple man’smodel and the integration of the time-dependent Schrödinger equation. We Vnd that absence or presenceof spectral interference indicate that plateau electrons primarily originate from either one or two timewindows with a duration of ∼ 450 as within the pulse. Photoelectrons that recollide with the surfacecan be controlled with attosecond precision, thus enabling attosecond science to be performed with awell-controlled nanoscale metal emitter. These electrons could serve as a probe of collective electrondynamics (e.g. plasmon polaritons) or trigger the generation of high-harmonic radiation. Our system alsorepresents a highly sensitive low-power sensor for the CEP.

[1] M. Schenk, M. Krüger, P. HommelhoU, Phys. Rev. Lett. 105, 257601 (2010).

[2] M. Krüger, M. Schenk, P. HommelhoU, submitted (2011).

53

P11 YIS Leif LaUerentz

Controlling the Growth of Covalent MolecularNetworks

L. LaUerentz1, V. Eberhardt2, C. Dri3, C. Africh3, G. Comelli3, F. Esch3, S. Hecht2, and L.Grill1

1Fritz Haber Institute of the Max Planck Society, Berlin2Department of Chemistry, Humboldt-Universität zu Berlin

3CNR-IOM Laboratorio TASC, Trieste

Recently it could be shown that promising structures can be formed by covalently connecting molecularbuilding blocks directly on surfaces [1]. Due to their chemical nature, these networks display high stabilityand potentially allow eXcient charge transport which makes them favorable for molecular electronicscompared to non-covalently bound structures.However, so far all of these structures resulted from one-step activation and connection procedures [2].This approach is limited with regard to the control of the network formation. For the fabrication of moresophisticated structures, e.g. the incorporation of functional units in deVned architectures, an increasedcontrol of the growth process is a prerequisite.We present a new strategy of 2D polymer construction on surfaces, which employs diUerent molecularside groups to steer the reaction pathway. Furthermore, the templating inWuence of a corrugated surfaceis studied. The potential of the approach is demonstrated by employing it to produce copolymers of highprecision.

[1] L. Grill et al., Nature Nanotech. 2, 687 (2007).

[2] A. Gourdon, Angew. Chem. Int. Ed. 47, 6950 (2008).

54

Felix Leyssner P12 YIS

Coverage and Temperature Dependent Isomerizationof an Imine Derivative on Au(111)

Felix Leyssner1, Mathias Koch1, Stephan Meyer1,Ying Luo2,Rainer Haag2, and PetraTegeder1

1Physics Department, Freie Universität Berlin, Arnimallee 14, Berlin, Germany2Chemistry Department, Freie Universität Berlin, Takustraße 3, Berlin, Germany

In this contribution high resolution electron energy loss spectroscopy (HREELS) is employed toanalyze thermally activated changes in the geometrical structure of the photochromic molecular switch3,3’,5,5’-tetra-tert-butyl-imine (TBI) adsorbed on Au(111). TBI in solution undergoes an optically inducedisomerization between a stable trans- and a metastable cis-isomer. For the analogical azobenzene derivative(TBA) on Au(111) it has already been shown that HREELS is an appropriate tool to investigate molecularswitching at surfaces, which goes along with signiVcant changes in the vibrational structure [1].Measurements have been performed for two coverage regimes: The monolayer and the bilayer regime.For both coverages all molecules are found in the trans state after deposition at sample temperaturesof T=210K, but conformational changes upon heating are observed, which are assigned to a switchingprocess, e.g. isomerization to the cis state. When heating the sample to T=440K two diUerent scenarios areobserved depending on the starting coverage: Annealing of a monolayer leads to an increasing numberof cis isomers, pointing towards an "inverted" thermal isomerisation behaviour, since it is known forthe molecule in solution that the trans isomer is the more stable compound which results in a thermallyactivated cis to trans relaxation [2]. Whereas for a bilayer the temperature induced isomerization of theTBI can be monitored as well, but desorption of the second layer at T=440K leads to the formation of atrans-monolayer.The fact that diUerent molecular conVgurations are found for equal coverages annealed at the sametemperature is highly surprising and shows that collective eUects may govern the switching properties ofmolecular switches on surfaces.

[1] L. Óvári et al., J. Phys. Chem. C 111, 42 (2007).

[2] J. Mielke et al., ACS Nano, in press, DOI: 10.1021/nn103297e.

55

P13 Manuel Ligges

Momentum-Resolved Fano-Resonances inTwo-Dimensional Surface States

Wai-lun Chan1, John Tritsch1, Andrei Dolocan1, Manuel Ligges1, Luis Miaja-Avila1,X.-Y. Zhu1

1Center for Nano and Molecular Science and Technology, University of Texas at Austin, Austin, TX, 78712

Fano resonance is a well-known quantum interference phenomenon that has been observed in manysystems. However, the interference eUect is mainly observed in the energy domain. Using monolayerof fullerene on Au(111) as a model system, we demonstrate that not only the interference eUect canoccur in two-dimensional (2D) surface/interfacial states, it can also be resolved spontaneously in theenergy and momentum domains. We use angle-resolved two-photo photoemission technique to study thetransient population of a series of 2D unoccupied states populated by femtosecond laser pulses. These2D bands have diUerent eUective masses and intersect with each other in the reciprocal space. At thepoints of intersection, we observe strong modulations in the transient population as a function of parallelmomentum vector. The population modulation in the reciprocal space can be explained by the well-knownFano resonances—the interference between diUerent quantum mechanical pathways in optical excitation.The experimental results agree semi-quantitatively with simulation based on optical Bloch’s equations.

56

Reinhard J. Maurer P14 YIS

Towards the Isomerization Dynamicsof Adsorbed Molecular Switches:

A ΔSCF Density-Functional Theory StudyReinhard J. Maurer1, Eva Deront1,2, Karsten Reuter1

1Lehrstuhl für Theoretische Chemie, Technische Universität München2Departément de Chimie, Ecole Normale Supérieure de Lyon

Stabilizing molecules at solid surfaces and switching them reversibly between deVned states would be akey component of a future molecular nanotechnology. Adsorption at metal surfaces is of particular interestas it could lead to novel functionality in form of isomerization mechanisms not present in gas-phaseor solution. Recent experiments indeed suggest such a photo-induced mechanism for tetra-tert-butylfunctionalized azobenzene (TBA) at Au(111) [1], involving electron transfer from the molecule to aphoto-excited hole in the metal 𝑑-band. Addressing this suggestion with Vrst-principles modeling requiresa numerically highly eXcient approach to make the calculations of photo-excited molecular motion at theextended surface tractable. To this end we explore a density-functional theory based Delta self-consistentVeld approach and assess its reliability for azobenzene in the gas phase against higher-level theory. Themethod predicts the overall topology of the corresponding photoisomerization pathways and the positionof decay funnels fairly well. This encourages us to discuss the isomerization of azobenzene and TBA inexcited states corresponding to the suggested hole-mechanism.

[1] S. Hagen et al., J. Chem. Phys. 129, 164102 (2008).

57

P15 YIS Michael Meyer

Ultrafast Electron Solvation Dynamicsat Alkali-Ion/Water Complexes

Michael Meyer1,2, Mathieu Bertin3, Uwe Bovensiepen4, Martin Wolf1,2

1Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany2Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abt. Physikalische Chemie, Faradayweg 4-6, 14195

Berlin, Germany3Université Pierre et Marie Curie Paris 6 - CNRS, Laboratoire de Physique Moléculaire pour l’Atmosphère

et l’Astrophysique, 4 place Jussieu, 75252 Paris cedex 05, France4Universität Duisburg-Essen, Fakultät für Physik, Lotharstr. 1, 47048 Duisburg, Germany

Radiation induced processes in molecular ice are of high relevance in numerous Velds, from atmosphericchemistry and astrochemistry to (photo) catalysis [1,2]. An excess charge in a polar environment, i.e. anelectron or an ion, is known to form a charge-solvent complex. We have studied the dynamics of electrontransfer and solvation dynamics in pure amorphous D2O layers [3] and alkali ion covered ice multilayerson metal surfaces using femtosecond time-resolved two-photon photoemission (2PPE) spectroscopy [4].In this study we have investigated the dynamics of the unoccupied alkali resonance of Na, Cs and K atomsadsorbed on the Cu(111) surface in the presence of low water coverages (up to 0.5 BL). In addition tothe well-known unoccupied alkali resonance [5] the coadsorption of small amounts of water leads to theappearance of a new feature in the 2PPE spectrum. We attribute this to an excess charge which is boundto an alkali/ice cluster. These trapped electrons Vrst appear at an equivalent of 3 D2O molecules per Csatom. They show a strong energetic stabilization of 1.3 eV/ps. With increasing water coverage, i.e. moremolecules available for molecular rearrangement, the decay time of the trapped electrons increases from41 fs for 3 D2O molecules per Cs atom to 62 fs for 9 D2O molecules per Cs atom assuming an exponentialdecay.

[1] B.C. Garret et al., Chem. Rev. 105, 355 (2005).

[2] Q.B. Lu, Physics Reports 487, 141 (2010).

[3] J. Stähler et al., Chem. Soc. Rev. 37, 2180 (2008).

[4] M. Meyer et al., J. Phys. Chem. 115, 204 (2011).

[5] J. Zhao et al., Phys. Rev. B 78, 085419 (2008).

58

Johannes Mielke P16 YIS

Conformational Switching of Porphyrin Derivativeson Au(111)

Johannes Mielke1, Felix Hanke2, Mats Persson2, Leonhard Grill1

1Fritz-Haber-Institut Berlin2University of Liverpool

The transport of information by conformational change in molecular nanostructures represents aninteresting alternative to charge transport, if in such a setup the conformation of one building block wouldbe coupled to that of the neighbouring one. Porphyrins are a very interesting class of molecules in thiscontext as they are known to adopt two conformations (planar and saddle shaped) in solution [1] and ona Au(111) surface [2]. Furthermore, the molecules assemble in close-packed islands on Au(111) and it hasbeen shown that by functionalisation with Br atoms, they can be covalently assembled into dimers, chainsor networks [3].

Regardless of the type of bonding, the molecules are still able to adopt the distinct conformations whichcan be distinguished in STM images, both at room temperature and at 5K and are identiVed by comparisonwith DFT calculations. It is investigated whether the conformations show a non-random distribution,which could be an indication for a coupling between neighbouring units. Furthermore it is possible toinduce a conformational change in the molecules, using thermal activation or manipulation with the STMtip. The dependence of this switching process on the conformation of the neighbouring molecules is alsoinvestigated.

[1] W. Jentzen et al., J. Phys. Chem. A 1997, 101, 5789

[2] V. Iancu et al., Nano Letters 6, 4, 820 (2006)

[3] L. Grill et al., Nature Nanotech. 2, 687 (2007)

59

P17 YIS Daniel Niesner

Image-Potential States of Grapheneon SiC(0001) and on Ir(111)

Daniel Niesner, Dieter Gugel, Thomas Fauster

Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstr. 7, 91058 Erlangen, Germany

Graphene can be produced epitaxially with high quality either by graphitization of SiC or by decompo-sition of hydrocarbons on metal substrates[1][2]. Two-photon photoemission (2PPE) experiments werecarried out on graphene on both semiconducting and metallic substrates. Infrared laser pulses from aTi:Sapphire laser system with a pulse duration of 37 fs serve as probe pulses and the third harmonic of thelaser output as pump pulses.

In case of freestanding graphene and graphene on large bandgap semiconductor substrate, image-potential states cannot be excited directly due to the lack of initial states. Nevertheless, two unoccupiedstates with binding energies of 250 meV and 110 meV can be observed for graphene on SiC.* Both statesshow a parabolic dispersion with an eUective mass close to the free electron mass. The lifetime of theenergetically lower state amounts to 45 fs which together with the larger lifetime of the higher-lying stateindicates that both are members of a series of image-potential states.

In case of graphene on Ir(111) the metal substrate provides initial electronic states for 2PPE. A series ofimage-potential states with a vanishing quantum defect and a parabolic dispersion with an eUective massclose to the free electron mass can be observed. Lifetimes of 35 fs, 114 fs and 270 fs of the lowest three statesare longer than for bare iridium and indicate a high degree of decoupling from the substrate. The intensitydistribution of the 𝑛 = 1 state observed in 2PPE shows a pronounced maximum at 𝑘|| = 0.15...0.2Å.From photoemission data, it can be attributed to a resonance with two downward-dispersing initialbands 230 meV and 450 meV below 𝐸𝐹 [3]. By increasing the photon energy, the 𝑛 = 2 state can alsobe shifted into resonance. Further evidence of a resonant transition is given by angle-resolved lifetimemeasurements.

[1] K. V. Emtsev et al., Nat. Mater. 8, 203 (2009).

[2] A. T. N’Diaye et al., Phys. Rev. Lett. 97, 215501 (2006).

[3] I. Pletikosić et al., J. Phys.: Condens. Matter 22, 135006 (2010).* We thank Th. Seyller and his group for providing the graphene/SiC samples.

60

J.C. Petersen P18 YIS

Momentum-Dependent Snapshotsof a Melting Charge Density Wave in 1T–TaS2

J.C. Petersen1,2, S. Kaiser2, N. Dean1, A. Simoncig2, H.Y. Liu2, A.L. Cavalieri2, C.Cacho3, I.C.E. Turcu3, E. Springate3, F. Frassetto4, L. Poletto4, S.S. Dhesi5, H. Berger6, A.

Cavalleri1,2

1Department of Physics, University of Oxford, Clarendon Laboratory, UK2Max Planck Department for Structural Dynamics, CFEL, Hamburg, Germany

3Central Laser Facility, STFC Rutherford Appleton Laboratory, Didcot, UK4CNR-Institute for Photonics and Nanotechnologies, Padova, Italy

5Diamond Light Source, Harwell Science and Innovation Campus, Didcot, UK6École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

Charge density waves [1] (CDWs) underpin the electronic properties of many complex materials [2–5].When electrons are uncorrelated, the electron-phonon interaction causes CDW order, with linearly coupledlattice and charge-density modulations that respond dynamically through amplitude and phase excitations.However, if electronic correlations set the dominant energy scale, the CDW may decouple from thelattice and respond on electronic time scales. 1𝑇–TaS2 is a controversial two-dimensional compoundwhose nested Fermi-surface geometry coexists with Mott physics. Here, we use time- and angle-resolvedphotoemission spectroscopy with sub-30-fs XUV pulses to map the time- and momentum-dependentelectronic structure after photo-excitation. CDW order, observed as a splitting between occupied sub-bands, melts well before the lattice responds, synchronously with Mott-gap collapse at the Fermi level.Our data challenge the view of the CDW as caused by Fermi surface nesting alone, and suggest thatcorrelations may be more important than previously thought in stabilizing charge order.

[1] G. Grüner, Density Waves in Solids (Perseus, 2004).

[2] F. Clerc, et al., J. Phys.: Condens. Matter 19 355002 (2007).

[3] M. Grioni, L. Perfetti, and H. Berger, Journal of Electron Spectroscopy and Related Phenomena 137-140417 (2004).

[4] G.H. Gweon, et al., Journal of Electron Spectroscopy and Related Phenomena 117-118 481 (2001).

[5] D. Jérome and H.J. Schulz, Adv. Phys. 31 299 (1982).

61

P19 Lukasz Piatkowski

Ultrafast Dynamics of Interfacial Water Revealed by2-Dimensional Surface Vibrational Spectroscopy

Lukasz Piatkowski, Zhen Zhang, Huib J. Bakker and Mischa Bonn

FOM-Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.

At the surface or interface of water, the water hydrogen-bonded network is abruptly interrupted,conferring properties on interfacial water diUerent from bulk water. Despite its importance for disciplinessuch as electrochemistry, atmospheric chemistry and membrane biophysics, the structure of interfacialwater has remained highly debated. We elucidate the structure and structural dynamics of interfacialwater using ultrafast two-dimensional surface-speciVc vibrational spectroscopy [1]. We present data forthe water-air and water-lipid interfaces, which reveal interfaces that are structurally heterogeneous, yethighly dynamical. We determine the timescale on which the heterogeneity decays and reveal the presenceof surprisingly rapid inter- and intramolecular energy transfer processes.

[1] J. Bredenbeck, A. Ghosh, H.K. Nienhuys, and M. Bonn, Acc. Chem. Res. 42 1332, (2009).

62

Laurenz Rettig P20 YIS

Time-Resolved Fermi Surface Mappingof a Charge Density Wave in RTe3

L. Rettig1,2, R. Cortés1,3, J.-H. Chu4, I.R. Fisher4, F. Schmitt4, P.S. Kirchmann5, R.G.Moore4, Z.-X. Shen4,5, M. Wolf3 and U. Bovensiepen2

1Freie Universität Berlin, Fachbereich Physik, Germany2Fakultät für Physik, Universität Duisburg-Essen, Germany

3Abteilung Physikalische Chemie, Fritz-Haber-Institut der MPG, Berlin, Germany4Department of Applied Physics, Stanford, USA

5Stanford Institute for Materials and Energy Science, Stanford, USA

The textbook-like charge density wave (CDW) formation in the family of rare earth tritelluridesRTe3 presents an excellent model system to study the eUects of order and broken symmetry in a highlycorrelated, low-dimensional model system. As revealed by angle-resolved photoemission (ARPES), largeenergy gaps open in the electronic bands below the CDW transition temperature, leading to the suppressionof large areas of the Fermi surface (FS) [1]. However, the underlying interactions like electron-electroncorrelation or electron-phonon interaction are diXcult to access by equilibrium methods like ARPES.Here, the use of non-equilibrium probes like time-resolved ARPES (trARPES) allows further insight on thedynamics linked to collective excitations of the broken symmetry state.

First experiments employing trARPES demonstrated the ultrafast melting of the CDW gapped state andthe excitation of the amplitude mode in TbTe3 [2]. Now, using a novel position-sensitive Time-of-Flightspectrometer (pTOF) [3], we are able to investigate the dynamics of both occupied and unoccupiedelectronic states over a contiguous area of the reciprocal space. Spectroscopy of the unoccupied bandsallows to strengthen further the scenario of FS nesting driven CDW formation suggested by ARPES [1].Furthermore, we can follow the evolution of the FS after optical excitation with fs time resolution andobserve the transition to a transient, ungapped state and closing of the FS within ∼200 fs.

In addition, the temperature dependence of the amplitude mode oscillation observed at low excitationWuences and its coherent control will be discussed.

[1] V. Brouet, et al., Phys. Rev. B 77, 235104 (2008).

[2] F. Schmitt, et al., Science 321, 1649 (2008).

[3] P. S. Kirchmann, et al., Appl. Phys. A 91, 211 (2008).

63

P21 YIS Christian Sohrt

Ultrafast Melting of a Charge-Ordered State in 1𝑇 -TaS2Investigated with Photoelectron Spectroscopy at FLASHChristian Sohrt1, Stefan Hellmann1, Martin Beye3, Timm Rohwer1, Florian Sorgenfrei2,Michael Bauer1, Alexander Föhlisch Wilfried Wurth2, Lutz Kipp1, and Kai Rossnagel1

1Institute of Experimental and Applied Physics, University of Kiel, Germany2Institute of Experimental Physics and Centre for Free-Electron Laser Science, University of Hamburg,

Germany3Helmholtz-Zentrum Berlin für Materialien und Energie, 12489 Berlin, Germany

The Free-Electron-Laser in Hamburg (FLASH) generates highly brilliant, ultrashort, and coherent pulsesin the XUV regime enabling many fascinating experiments. Various challenges concerning space-chargeeUects as well as timing and synchronization issues have recently been solved. Now optical pump-XUVprobe photoelectron spectroscopy on solid surfaces is possible over a wide probing photon energy rangewith time and energy resolutions of ∼700 fs and ∼300 meV, respectively. Our most recent experiments,performed on the correlated layer compound 1𝑇 -TaS2 deep in the charge-density-wave (CDW) state,demonstrate that core-level dynamics on the femto-, pico- and nanosecond time scale can be investigatedat FLASH. We Vnd that long-range charge order in 1𝑇 -TaS2 collapses promptly and that a domain-likeCDW state is reached within about 1 ps. The results imply that the CDW and the accompanying periodiclattice distortion, which are strongly coupled in equilibrium, are decoupled after photoexcitation on thetime scale for electron-phonon thermalization. [1]

[1] S. Hellmann et al., Phys. Rev. Lett. 105, 187401 (2010).

64

Ankatrin Stange P22 YIS

Time- and Angle-Resolved Photoemission with HighHarmonic Light Pulses: Experimental RealizationAnkatrin Stange, Stefan Hellmann, Timm Rohwer, Christian Sohrt, Martin

Wiesenmayer, Kerstin HanU, Matthias Kalläne, Lutz Kipp, Michael Bauer, Kai Rossnagel

Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24118 Kiel,Germany

Angle-resolved photoelectron spectroscopy (ARPES) has proved to be a leading technique in identifyingstatic key properties of complex electron systems. In a pump probe scheme using femtosecond light pulsesthis technique can be extended to monitor ultrafast changes in the electronic valence structure in responseto an intense optical excitation [1]. Here we present an experimental setup for time-resolved ARPES usingfemtosecond XUV probe pulses. We will focus on the relevant details and speciVcations of the system suchas time and energy resolution. We show that the application of XUV pulses is particularly advantageousin recording valence structure transients at large momentum values in the vicinity or even beyond theborder of the Brillioun zone. The capabilities of the setup will be illustrated by selected experimentalexamples. We will also discuss potential future developments regarding issues such as photon energyrange and energy resolution.

[1] F. Schmitt et al., Science 321, 1649 (2008).

65

P23 YIS Simon Wall

Ultrafast Changes in Lattice Symmetry Probed byCoherent Phonons

S. Wall1, D. Wegkamp1, L. Foglia1, K. Appavoo2,R. F. Haglund2, J. Stähler1, M. Wolf1

1Fritz Haber Institute of the Max Planck Society, Department of Physical Chemistry, Faradayweg 4-6, 14195Berlin, Germany

2Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235-1807, USA

We present a new technique to measure ultrafast changes in the symmetry of the lattice potentialinitiated by a laser pulse. By performing pump-pump-probe measurements we detect changes in thecoherent lattice response, which allows us to deduce symmetry changes on a sub-phonon-period timescale.This technique is applied to the photoinduced phase transition in VO2, where a rapid change in thelattice response is observed when the sample is excited above the phase transition threshold, indicating anelectronically driven change in potential symmetry.

66

List of Participants

Martin Aeschlimann

Dept. of PhysicsTechnische Universität KaiserslauternE. Schroedinger Str. 4667663 KaiserslauternGermany

t+49 (0)631 205 2322

� ma@physik.uni-kl.de

Michael Bauer

Institut für Experimentelle und AngewandtePhysik (IEAP)Christian-Albrechts-Universität zu KielLeibnizstraße 1924118 KielGermany

t+49 (0)431 880 5098

� bauer@physik.uni-kiel.de

Martin Beye

Helmholtz Zentrum BerlinAlbert-Einstein-Str. 1512489 BerlinGermany

t+49 (0)177 318 5598

� martin.beye@helmholtz-berlin.de

Uwe Bovensiepen

Dept. of PhysicsUniversity Duisburg-EssenLotharstr. 147048 DuisburgGermany

t+49 (0)203 379 4533

� uwe.bovensiepen@uni-due.de

Daniele Brida

Dept. of PhysicsUniversity of KonstanzPO box M 69678457 KonstanzGermany

t+49 (0)7531 882 936

� Daniele.Brida@uni-konstanz.de

Christopher Bronner

Dept. of PhysicsFreie Universität BerlinArnimallee 1414195 BerlinGermany

t+49 (0)30 838 52157

� bronner@zedat.fu-berlin.de

Robert Carley

Dept. A1Max-Born-InstitutMax-Born-Str. 2A12489 BerlinGermany

t+49 (0)30 6392 1212

� carley@mbi-berlin.de

Andrea Cavalleri

Max Planck Research Department for StructuralDynamicsUniversity of Hamburg, CFELc/o DESY, Geb. 49Notkestrasse 8522607 HamburgGermany

t+49 (0)40 8998 5354

� andrea.cavalleri@mpsd.cfel.de

List of Participants

Jan-Christoph Deinert

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5434

� deinert@fhi-berlin.mpg.de

Pedro M. Echenique

Dpto. de Física de Materiales UPV/EHUFacultad de Ciencias Químicas UPV/EHU)Apdo. 1.07220080 Donostia-San SebastiánBasque Country, Spain

t+34 (0)943 01 596

� wapetlap@sq.ehu.es

Ralph Ernstorfer

Department of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5117

� ernstorfer@fhi-berlin.mpg.de

Björn Frietsch

Dept. A1Max-Born-InstitutMax-Born-Str. 2A12489 Berlint+49 (0)157 845 51983

� frietsch@mbi-berlin.de

Christian Frischkorn

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5230

� christian.frischkorn@fu-berlin.de

Cornelius Gahl

Dept. of PhysicsFreie Universität BerlinArnimallee 1414195 BerlinGermany

t+49 (0)30 6392 1218

� gahl@mbi-berlin.de

Leonhard Grill

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5108

� lgr@fhi-berlin.mpg.de

Kerstin HanU

Institut für Experimentelle und AngewandtePhysik (IEAP)Christian-Albrechts-Universität zu KielOlshausenstr. 4024098 KielGermany

t+49 (0)431 880 3823

� hanU@physik.uni-kiel.de

Tony F. Heinz

Dept. of PhysicsColumbia University538 West 120th St.New York, NY 10027USA

t+1 212 854 6564

� tfh3@columbia.edu

Dirk Heitepriem

Research in Motion / BlackberryGovernment Relations Manager Germanyt+49 (0)30 520 0057 7910

� dheitepriem@rim.com

68

List of Participants

Tobias Hertel

Institut für Physikalische und TheoretischeChemieJulius-Maximilians-Universität WürzburgAm Hubland97074 WürzburgGermany

t+49 (0)931 31 86301

� tobias.hertel@uni-wuerzburg.de

Ulrich Höfer

Dept. of PhysicsPhilipps-Universität MarburgRenthof 535032 MarburgGermany

t+49 (0)6421 28 24215

� hoefer@physik.uni-marburg.de

Tian Huang

Dept. of Physics and AstronomyUniversity of Pittsburgh3941 O’Hara St.Pittsburgh, PA, 15260USA

t+1 412 624 9577

� tih14@pitt.edu

Rupert Huber

Dept. of PhysicsUniversity of RegensburgUniversitätsstraße 3193053 RegensburgGermany

t+49 (0)941 943 2070

� rupert.huber@physik.uni-regensburg.de

Dirk Jannick

Fritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)170 337 8223

� jannick@fhi-berlin.mpg.de

Thorsten Kampen

SPECS Surface Nano Analysis GmbHVoltastraße 513355 BerlinGermany

t+49 (0)30 467 824 9330

� t.kampen@specs.de

Tobias Kampfrath

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5222

� kampfrath@fhi-berlin.mpg.de

Reinhard Kienberger

Fachgebiet für Experimentalphysik E11aTechnische Universität MünchenJames-Franck-Str. 185748 GarchingGermany

t+49 (0)89 289 12837

� reinhard.kienberger@tum.de

Patrick Kirchmann

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5127

� kirchmann@fhi-berlin.mpg.de

Harald Kirsch

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5232

� Kirsch85@fhi-berlin.mpg.de

69

List of Participants

Michael Krüger

Max-Planck-Institut für QuantenoptikHans-Kopfermann-Str. 185748 GarchingGermany

t+49 (0)89 32905 769

�Michael.Krueger@mpq.mpg.de

Leif LaUerentz

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5110

� leif.laUerentz@fhi-berlin.mpg.de

Alfred Leitenstorfer

Dept. of PhysicsUniversity of KonstanzPO box M 69578457 KonstanzGermany

t+49 (0)7531 88 3818

� alfred.leitenstorfer@uni-konstanz.de

Felix Leyssner

Dept. of PhysicsFreie Universität BerlinArnimallee 1414195 BerlinGermany

t+49 (0)30 838 53340

� felix.leyssner@physik.fu-berlin.de

Manuel Ligges

Dept. of PhysicsUniversity Duisburg-EssenLotharstr. 147048 DuisburgGermany

t+49 (0)203 379 4531

� manuel.ligges@uni-due.de

Martin Lisowski

Femtolasers Produktions GmbHFernkorngasse 101100 ViennaAustria

t+43 1503 70020

� martin.lisowski@femtolasers.com

Dirk Manske

Max-Planck-Institut für Festkörperforschung (MPI-FKF)Heisenbergstr. 170569 StuttgartGermany

t+49 (0)711 689 1552

� D.Manske@fkf.mpg.de

Reinhard J. Maurer

Technische Universität MünchenLichtenbergstr. 485747 GarchingGermany

t+49 (0)89 289 13627

� reinhard.maurer@ch.tum.de

Alexey Melnikov

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5113

� melnikov@fhi-berlin.mpg.de

Michael Meyer

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 838 56059

� meyerm@fhi-berlin.mpg.de

70

List of Participants

Johannes Mielke

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5110

� mielke@fhi-berlin.mpg.de

R.J. Dwayne Miller

Max Planck Research Group for Atomically Re-solved DynamicsDept. of PhysicsUniversity of Hamburg, CFELc/o DESY, Geb. 49Notkestrasse 8522607 HamburgGermany

t+49 (0)40 8998 1958

� dwayne.miller@mpsd.cfel.de

Karina Morgenstern

Division of Atomic and Molecular Structures(ATMOS)Institut für FestkörperphysikLeibniz University of HannoverAppelstraße 230167 HannoverGermany

t+49 (0)511 762 4821

� morgenstern@fkp.uni-hannover.de

Margaret Murnane

JILAUniversity of ColoradoBoulder, CO 80309USA

t+1 303 492 7839

� murnane@jila.colorado.edu

Daniel Niesner

Universität Erlangen-NürnbergStaudtstraße 7, A391058 ErlangenGermany

t+49 (0)9131 85 28414

� daniel.niesner@physik.uni-erlangen.de

Anders Nilsson

SSRL FacultyStanford University2575 Sand Hill Road, MS69Menlo Park, CA 94025USA

t+1 650 926 2233

� nilsson@slac.stanford.edu

Luca Perfetti

École Polytechnique91128 Palaiseau cedexParisFrance

t+33 (0)169 334 556

� luca.perfetti@polytechnique.edu

Hrvoje Petek

Dept. of Physics and AstronomyUniversity of Pittsburgh3941 O’Hara St.Pittsburgh, PA 15260USA

t+1 412 624 3599

� petek@pitt.edu

Jesse Petersen

Dept. of PhysicsClarendon LaboratoryUniversity of OxfordParks RoadOxford OX1 3PUUnited Kingdom

t+44 186 527 2301

� j.petersen1@physics.ox.ac.uk

71

List of Participants

Lukasz Piatkowski

FOM Institute - AMOLFScience Park 1041098 XG AmsterdamNetherlands

t+31 207 547 100

� piatkowski@amolf.nl

Laurenz Rettig

Dept. of PhysicsUniversity Duisburg-EssenLotharstr. 1

47048 DuisburgGermany

t+49 (0)30 838 54629

� rettig@physik.fu-berlin.de

Karsten Reuter

Technische Universität MünchenLichtenbergstr. 485747 GarchingGermany

t+49 (0)89 289 13616

� karsten.reuter@ch.tum.de

Lutz Richter

Research in Motion / BlackberryUni Tech CentreUniversitätsstraße 14044799 BochumGermany

t+49 (0)151 1134 3131

� lrichter@rim.com

Angel Rubio

European Theoretical Spectroscopy Facility (ETSF)Centro Joxe Mari KortaAvenida de Tolosa, 7220018 Donostia-San SebastiánSpain

t+34 94301 8292

� angel.rubio@ehu.es

Peter Saalfrank

Institute of ChemistryUniversity of PotsdamKarl-Liebknecht-Str. 24/25, Haus 2514476 Potsdam-GolmGermany

t+49 (0)331 977 5232

� petsaal@rz.uni-potsdam.de

Christian Sohrt

Institut für Experimentelle und AngewandtePhysik (IEAP)Christian-Albrechts-Universität zu KielOlshausenstr. 4024098 KielGermany

t+49 (0)431 880 3863

� sohrt@physik.uni-kiel.de

Ankatrin Stange

Institut für Experimentelle und AngewandtePhysik (IEAP)Christian-Albrechts-Universität zu KielLeibnizstraße 1924118 KielGermany

t+49 (0)431 880 1998

� stange@physik.uni-kiel.de

Julia Stähler

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5125

� staehler@fhi-berlin.mpg.de

72

List of Participants

Petra Tegeder

Dept. of PhysicsFreie Universität BerlinArnimallee 1414195 BerlinGermany

t+49 (0)30 838 56234

� petra.tegeder@physik.fu-berlin.de

Simon Wall

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5432

� wall@fhi-berlin.mpg.de

Martin Weinelt

Dept. of PhysicsFreie Universität BerlinArnimallee 1414195 BerlinGermany

t+49 (0)30 838 53341

� weinelt@physik.fu-berlin.de

Martin Wolf

Dept. of Physical ChemistryFritz-Haber-Institut der Max-Planck-GesellschaftFaradayweg 4–614195 BerlinGermany

t+49 (0)30 8413 5111

� wolf@fhi-berlin.mpg.de

Xiaoyang Zhu

Dept. of Chemistry and BiochemistryUniversity of Texas1 University Station A5300Austin, TX 78712-0165USA

t+1 471 9914

� zhu@cm.utexas.edu

73

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