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Ab-initio study of electric field effect on black phosphorus - PowerPoint PPT Presentation
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Theory and Simulation of Materials
Dr. Kapildeb Dolui
National University of Singapore
Possible doping strategies in monolayer MoS2
VB VB VB VBVB
CBCB
CB
CB
CB
1.90 eV[1] 1.87 eV
2.87 eV2.23 eV
1.80 eV
Expt. LDA HSE06 scGW BSE
Effect of substrate Effect of doping
Absorption
Substitutional doping
Formation energies
SiO2
MoS2
Kapildeb Dolui et al. Phys. Rev. B 87, 165402 (2013); Phys. Rev. B 88, 075420 (2013);
Exciton binding energy: 1.1 eV (monolayer), 0.11 eV (bulk) [2]
[1] Phys. Rev. Lett. 105, 136805 (2010); [2] Phys. Rev. B 86, 241201 (R) (2012)
Impurity at the surface of substrate can change the conductivity of a monolayer MoS2 Nb substitution and alkaliatomabosortion are sutiable candidates as ptype and ntype dopant,respectively
Tunable electronic structure of 2D materials
Effect of perpendicular electric field on few layer black phosphorus
Effect of transverse electric field on monolayer MoS2 nanoribbon
The bandgap of MoS2 nanoribbon can be tuned by applying an external electric field. Semiconductor to metal transition occurs at a critical field, which decreases with the size of nanoribbon.
The bandgap of few layer black phosphorus can be tuned by applying an external electric field. Semiconductor to metal transition occurs at a critical field, which decreases with the thickness of black phosphorus. Interestingly, beyond critical field the system becomes Dirac semimetal due to the anisotropic interaction bewteen the layers.
Kapildeb Dolui et al. ACS Nano 6, 4823 (2012); Scientific Reports 5, 11699 (2015)
Dimensionality driven CDW phase in TiS2 Lattice instability Criteria:
= electronphonon couplingUq = columb interactionVq = exchnage interaction = elctronic bare suceptibilityχq
gq
Charge Density Wave (CDW):
Phonon bandstructure
Electronic structure
we observe a Kohn anomaly in the bulk phonon dispersion. In contrast, a monolayer TiS2 exhibits a CDW instability at the M point in the Brillouin zone, resulting in the formation of 2×2 superstructure.
Atomic distortions
Kapildeb Dolui et al. arXiv preprint arXiv:1310.1866
bulk monolayer
Renormalization of molecular electronic levels
Benzene
Quasiparticle (G0W0) HOMOLUMO gap
Benzene@BNGraphite
Benzene@BN
Benzene@Graphite
10.72 eV8.61 eV
7.36eV 7.23eV
The DFTLDA gap of benzene molecule almost reamins same 5.0 eV for all the considered inteface caseses. Our calculations including many body effects (with in the G0W0 approximation) show that dynamical polarization effects renormalize molecular interface states. The effect of polarization is to reduce the gap between occupied and unoccupied molecular orbitals. Interestingly, 2D semiconducting spacer participate largely in screening and can be used to tune the molecule's gap.
Graphite | BN | Benzene
Metal | spacer | molecule
Molecule absorbed in metal interface Benzene at 2D hetrostructure
Kapildeb Dolui et al. (manuscript in prepration)
Prediction of Dirac materials
We explore a new idea for the formation of bulk Dirac cones and Weyl orbital semimetals without the need of spin orbit coupling (SOC) or structural confinement. Weyl orbital semimetals can be constructed for various combinations of different orbitals, such as even and odd orbitals pair or bonding and antibonding states or pair of even or pair of odd orbitals or two different basis of same orbital, in variety of 3D lattice.
Interorbital hopping term:
Example:
Kapildeb Dolui et al. arXiv preprint arXiv:1412.2607
Transport in 2D materials
Experiment @ Fundan University, China
Theory
Lead | Channel | Lead
Magnetoregistance
Kapildeb Dolui et al. Phys. Rev. B 90, 041401(R) (2014); Nano Lett. 15, 5261(2015)
Our firstprinciples transport calculations are performed using the SMEAGOL code, which integrates the nonequilibrium Green’s function method for electron transport with density functional theory.
We have dismostration a giant magnetoresistance (MR) effect in Fe/MoS2/Fe junctions. This a first demostration of magnetoregistance in 2D chalcogenides. Our prediction of magenetoregistnace is confirmed by the experimental measurements.
TT = transmission
(Fe) (MoS2) (Fe)