Electron-phonon and spin-orbit coupling in MoS2

Date: 19 January 2016

Venue: UAntwerp - Campus Groenenborger - Room U.241 - Groenenborgerlaan 171 - 2020 Antwerp

Time: 4:00 PM - 5:00 PM

Organization / co-organization: Condensed Matter Theory (CMT)

Short description: 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. [1]

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.

[1] A. Molina-Sánchez, K. Hummer, L. Wirtz, Surface Science Reports 70, 554 (2015).

Contact email: lucian.covaci@uantwerp.be

Link: https://www.uantwerpen.be/cmt