SKM 2021 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 4: 2D materials and their heterostructures (joint session DS/CPP/HL)
HL 4.1: Talk
Monday, September 27, 2021, 11:15–11:30, H3
Tunable phases of Moire excitons in van der Waals heterostructures — •Samuel Brem1, Christopher Linderälv2, Paul Erhart2, and Ermin Malic1,2 — 1Philipps University, Marburg, Germany — 2Chalmers University of Technology, Göteborg, Sweden
Two monolayers of Transition Metal Dichalogenides can be vertically stacked to form a type-II heterostructure, hosting spatially indirect interlayer excitons. Recent studies have shown that moire superlattices can be created by stacking monolayers with a finite twist-angle, giving rise to a tunable modification of exciton features in optical spectra. The moire patterns lead to a spatially varying band gap and consequently, excitons experience a periodic potential modifying their transport properties.
We have combined first-principles calculations with the excitonic density matrix formalism to develop an exciton model for small-angle twisted MoSe2/WSe2 heterostructures. Based on a microscopic approach, we calculate the band structure and wave functions of intra- and interlayer excitons within a twist-tunable moire lattice as well as the resulting optical response. For a range of small twist-angles, we predict completely flat exciton bands corresponding to moire trapped, localized quantum emitters. However, we reveal that this moire exciton phase quickly changes with increasing twist-angle, and at 3°, there are only delocalized excitons. We find the emergence of multiple moire exciton peaks in the absorption, whose spectral shifts with varying twist-angle are characteristic for the trapped or delocalized phase.