Regensburg 2019 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 17: Two-dimensional Materials I (joint session HL/CPP)
HL 17.11: Talk
Tuesday, April 2, 2019, 12:15–12:30, H36
Excitation-Induced Transition from Direct to Indirect Band Gaps in Monolayer TMDs — •Daniel Erben1, Alexander Steinhoff1, Michael Lorke1,2, Tim Wehling1,2, Christopher Gies1, and Frank Jahnke1 — 1Institute for Theoretical Physics, University of Bremen — 2Bremen Center for Computational Materials Science, University of Bremen
Monolayers of transition metal dichalcogenides (TMDs) show exceptionally strong Coulomb interaction between charge carriers due to the small thickness and weak dielectric screening. Many-body interactions induced by excited charge carriers directly influence the electronic and optical properties in these materials. Strong many-particle renormalizations caused by the Coulomb interaction of the excited carriers will be discussed for MoS2, MoSe2, WS2 and WSe2. We solve the semiconductor Bloch equations on the full Brillouin zone using ab-initio band structures and interaction matrix elements.
Large excitation-dependent band-gap renormalizations are found. In all four materials, the conduction band Σ-valley exhibits a stronger shift to lower energies than the K-valley. As a result, all four TMDs show a tendency to become more indirect or even undergo a transition from a direct to indirect band gap with increasing excited carrier density.
For optical excitation of monolayer TMDs, we also study the connection between pump fluence and excited carrier density. The contributions of various many-body effects to a strong non-linearity are identified.