Electron-phonon and spin-orbit coupling in MoS2
19 januari 2016
UAntwerp - Campus Groenenborger - Room U.241 - Groenenborgerlaan 171 - 2020 Antwerp
16 - 17 uur
Organisatie / co-organisatie:
Condensed Matter Theory (CMT)
Physics Department Seminar by Prof Ludger Wirtz, University of Luxemburg
Recently, many research groups have been performing detailed spectroscopy experiments on single and multi-layer transition metal dichalcogenides (TMDs). A precise quantitative understanding of the electronic structure and the vibrational modes is necessary for a correct interpretation of the experiments. I will give an overview from the theoretical perspective. 
We summarize the ample literature on quasi-particle band-structures of semiconducting TMDs where spin-orbit coupling plays an important role. Calculations of optical absorption spectra on the level of the Bethe-Salpeter equation display a variety of excitonic effects (enhanced by the 2D nature of the system and influenced by the substrate): a series of bound excitons as well as higher-lying excitons in resonance with the continuum of electron-hole pair transitions. Including electron-phonon coupling in order to simulate spectra at finite temperature, we find that bound excitons (A and B peaks) and resonant excitons (C peak) exhibit different behavior with temperature, displaying different non-radiative lifetimes. We conclude that the inhomogeneous broadening of the absorption spectra is mainly due to electron-phonon scattering mechanisms. Our calculations explain the shortcomings of previous (zero-temperature) theoretical spectra and match well with the experimental spectra acquired at room temperature.
Finally, we shall give an outlook on the calculation of resonant Raman spectra of single and multi-layer MoS2 via a finite-difference calculation of the polarizability of the system including excitonic effects on the level of the Bethe-Salpeter equation.
 A. Molina-Sánchez, K. Hummer, L. Wirtz, Surface Science Reports 70, 554 (2015).
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