Twist versus heterostrain control of optical properties of moir\'e exciton minibands

TL;DR

This paper compares the optical properties of moiré exciton minibands in heterobilayer transition metal dichalcogenides caused by heterostrain versus twisting, revealing distinct dispersion, polarization, and evolution behaviors.

Contribution

It introduces a detailed analysis of how heterostrain and twisting differently affect exciton miniband dispersions, polarization, and optical properties in moiré superlattices.

Findings

Heterostrain shifts exciton dispersion via gauge potential effects.

Strain breaks three-fold symmetry, leading to elliptically polarized valley optical selection.

Excitonic wavefunctions evolve from localized to extended states with decreasing moiré period.

Abstract

We investigate the optical properties of interlayer excitons in heterobilayer transition metal dichalcogenides where moir\'e pattern is introduced by heterostrain, in comparison with that introduced by twisting (and/or lattice mismatch). Besides being a cause of the moir\'e texture, strain also effectively introduces a constant gauge potential on either electron or hole, which shifts the dispersion of kinetic energy with respect to the excitonic crystal momenta in the moir\'e superlattices.This leads to distinct exciton mini-band dispersions and light coupling properties from the twisting induced moir\'e, even if the excitonic moir\'e superlattice potentials have the similar real-space profile for the two cases. For strain that breaks the three-fold rotational symmetry at the atomic scale,the exciton wave packets trapped at the superlattice potential minima have elliptically polarized valley optical selection rules, in contrast to the circularly polarized ones in the twisting moir\'e. We investigate the evolution of the excitonic mini-bands and the optical dipoles of the bright states inside the light cones with the decrease of the moir\'e periodicity, upon which the excitonic wavefunctions evolve from localized wave packets to the extended Bloch states. Furthermore, moir\'e exciton properties under the interplay of twisting and heterostrain are also discussed.