Freie Universität Berlin FKF-MPG 20.Nov.2013 1/22

STS in a superconducting

junction

and the

ac-Josephson

effect: A new type of spectroscopy

Klaus Klaus BaberschkeBaberschkeInstitut fInstitut füür Experimentalphysikr Experimentalphysik

Freie UniversitFreie Universitäät Berlint Berlin Arnimallee 14 DArnimallee 14 D--14195 Berlin14195 Berlin--Dahlem Dahlem

GermanyGermany

e-mail: bab@physik.fu-berlin.dehttp://www.physik.fu-berlin.de/~bab

1.

Quasi particle tunneling2.

Josephson effect = pair tunneling, dc, ac

3.

Our ac Josephson spectroscopy (~30 years ago)4.

Proposal for a new ac Josephson UHV-LT-STS

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Rev.Sci.Inst.84,22903(2013)

Single electron

tunneling

(quasi particle)

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2Δ

=3.5 kB

TC

; U

mV 10 K 860 µeV

That’s what w

e do NOT discussKondo-resonance on TTF-TCNQ/Au(111) PRL 101, 217203 (2008)

S-S junction N-N junction

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Coupled

superconductors

SIS, SNS

L,R

2

= , Cooper pair density

order parameter

We used : N = Au + rare earth

You may use: I = molecule monolayer

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dc

-Josephson

effect

= pair tunneling

J0

h = 2T (L

R

)1/2

Φ0

= hc/2e

210-7

G cm2

Overlap of L

and R

.

pair wave fct. leads to a tunnel current of Cooper pairs.

*

This leads to flux quantization and Fresnel interference pattern

–

not discussed today.

It’s a new particle with 2e , 2m and S=0

with Bose statistic.

is one macroscopic

wave fct

for all Cooper pairs.*

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Tunnel junction

+ voltage

= ac

Josephson

effect

J = J0

sin(ΔΘ-2eVt/h) hν

= 2eV

483.6 MHz 1µV

NS1 S2

V

eVt 212

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Our

ac

Josephson

spectroscopy

We

worked

with

a tip

and film thickness of r and d of few

µm, R

0.5 Ω

ac-Josephson

effect as MW-generator

and current

as detector

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Proof for a good Josephson junction:

Fraundofer

diffraction pattern:

I ≈

cos

(πΦ/Φ0

)

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VRi

RVi c

tot 2

2

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For ac Jospheson

effects

see standard literature

books by

P. G. de Genne

1964

M. Tinkham

1996

A. Barone

1982

Rf-driven

Junctions Shapiro

steps

Photon-assisted

tunneling

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483,6 MHz = 1V

Gd3+

=> 8S7/2 => 2S+1 = 8

Crystal field

splitting

cubic

or

lower

symmetry

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Hyperfine splitting of Au 167Er, S + I = F = 3 and 4

ΔEtheo

= 2.87 GHz ; Vres

= 5.4(2) µV, νres

=2.6(1) GHz

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Proposal for new ac Josephson UHV-LT-STSFe3+ S=5/2

Fe3+ or Fe2+,

HS or LS,finally there will be some ZFS within the (2S+1) manifold

Molecular monolayer and superconductingtip and substrate crystal,e.g. Pb.

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3dn-energy scheme and magnetism of the Fe-ion

Dramatic change of ligand

field upon coadsorption

of oxygen.

Gambardella et al. 2009, Bernien

et al. 2009

Unperturbed eg

, t2g

eigenstatesare no good.

“zero field splitting”

≡

CEF

Fe 3+,2+

S= 5/2, 3/2, 1/2S= 2, 1, 0

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Zero field splitting:For Cr3+

=> S=3/2, in Al2

O3

--------------------------------For Fe3+

=> S=5/2Splitting in E±1/2

, E±3/2

,E±5/2

ΔE = 2D, 4DRange 5 to 40 GHz, Bittl

paper

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LZ • SZ

+L •

S

L±

• S+_

The

orbital moment

is

quenched in cubic

symmetry

2-

LZ

2-

= 0,

but

not

for

tetragonal symmetry

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1. Magnetic anisotropy energy = f(T)

2. Anisotropic magnetic moment

f(T)

B (G)

100

100 20000

500

300

300

M (G

)

[111]

[100]

Ni[100]

[111]

0.1 GL ~~

K. Baberschke, Lecture Notes in Physics, Springer 580, 27 (2001)

LS4µB

anisotropic

µL

MAE

MAE µL Bruno (‘89)

g|| - g

= ge (

-|| )

D= gge

Magnetic Anisotropy Energy (MAE) and anisotropic µL

Orbital magnetic

moments

are

small, but

all important

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100µV

48 GHz

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variable frequencies

0.5 –

50 GHz are

needed

to measure CFS with

and without

magnetic

fields

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Alexander Schnegg

et al.Phys. Chem. Chem. Phys., 11, 6820 (2009)

Frequency

domain

Fourier

transform

THz-EPR

on single molecule

magnets

using

coherent

synchrotron

radiation

Frequency domain Fourier transform THz electron paramagnetic resonance (FD-FT THz-EPR) based on coherent synchrotron radiation (CSR) is presented as a novel tool …. at the BESSY II storage ring …

in a frequency range from

5 cm-1

up to 40 cm-1

… together with first measurements on the SMM Mn12

Ac where ΔMS

= ±1 spin transition

was studied …. Thank you

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