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In-plane charge-transfer excitons in near-60° twisted bilayer WS<sub>2</sub>: a first-principles GW-BSE study

ORAL

Abstract

Moiré superlattices based on monolayer transition metal dichalcogenides host exotic excitonic states of qualitatively different character from the individual layers. Twisted homobilayer transition metal dichalcogenides are known to host flat electronic bands at the valence and conduction band edges for twist-angles close to 60°, whose spatial modulation can be described by solutions of a particle in a triangular quantum well. Here, we extend the pristine unit-cell matrix projection (PUMP) [1] approach to study the GW-BSE spectrum of a 57.7° twisted bilayer WS2, with 4000 atoms in the moiré unit-cell, including spin-orbit coupling effects. We discover the lowest-energy exciton to be a layer-hybridized exciton with in-plane charge transfer character, with the photoexcited holes derived from the Γ valley and the photoexcited electrons from the K valley in the pristine unit-cell BZ. Furthermore, the higher energy excitonic states possess highly non-trivial characters, being strongly influenced by the spatial modulation of the valence states due to the triangular quantum well potential.

[1] M. H. Naik, E. C. Regan, Z. Zhang, …, F. H. Jornada, F. Wang, S. G. Louie, Nature 609, 52–57 (2022)

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Presenters

  • Mit H Naik

    University of California, Berkeley, University of California at Berkeley and Lawrence Berkeley National Lab, University of California at Berkeley; Lawrence Berkeley National Lab

Authors

  • Mit H Naik

    University of California, Berkeley, University of California at Berkeley and Lawrence Berkeley National Lab, University of California at Berkeley; Lawrence Berkeley National Lab

  • Woochang Kim

    University of California at Berkeley and Lawrence Berkeley National Lab, University of California, Berkeley

  • Zhenglu Li

    Lawrence Berkeley National Laboratory, University of California at Berkeley, and Lawrence Berkeley National Laboratory

  • Felipe H da Jornada

    Stanford University, Stanford

  • Steven G Louie

    University of California at Berkeley, University of California, Berkeley, University Of California, Berkeley, University of California at Berkeley and Lawrence Berkeley National Lab, University of California at Berkeley; Lawrence Berkeley National Lab, UC Berkeley, University of California at Berkeley, and Lawrence Berkeley National Laboratory, UC berkeley, Lawrence Berkeley National Laboratory, Physics Department, UC Berkeley and Lawrence Berkeley National Lab, Department of Physics, University of California at Berkeley and Materials Sciences Division, Lawrence Berkeley National Laboratory, LBNL & UC Berkeley