Dresden 2017 – scientific programme
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O: Fachverband Oberflächenphysik
O 77: 2D Materials Beyond Graphene IV
O 77.4: Talk
Wednesday, March 22, 2017, 16:00–16:15, WIL A317
A many-body view on the not-so-passive role of the substrate: trions and screening in transition metal dichalcogenides — •Matthias Drüppel1, Thorsten Deilmann2, Peter Krüger1, and Michael Rohlfing1 — 1Institut für Festkörpertheorie, Westfälische Wilhelms-Universität, 48149 Münster, Germany — 2Center for Atomic-Scale Materials Design (CAMD), Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
The strongly enhanced Coulomb interaction due to reduced dimensionality has established transition metal dichalcogenides (TMDC) as promising candidates for next-generation opto-electronic devices. However, in almost all experiments and applications, the monolayer is deposited on a substrate for mechanical stability or - in bulk/few layer materials - interacts with neighboring layers. In this talk we show that the surrounding of the monolayer does not play a passive role. In contrast, it distinctly modifies the TMDC excitations.
We subsequently apply DFT → GW → Bethe-Salpeter equation (BSE) to access the optical properties. Our results show how additional charge carriers, that are often induced by substrates, lead to trion formation that might dominate optical spectra. We take our ab-initio approach and directly compare trion and exciton spectra, finding that trions split into inter- and intra-valley trions. Additionally, a drastically enhanced screening by a substrate renormalizes both the exciton and trion binding energies and the fundamental band gap. In bilayer and bulk materials, excitons can be excited with electron and hole located on different layers, forming inter-layer excitons.