Strain Correlated Linearly Polarized Photoluminescence in WS2/WSe2 Moir\'e Superlattices

TL;DR

This study demonstrates that strain, rather than valley coherence, primarily influences linearly polarized photoluminescence in WS2/WSe2 moiré superlattices, highlighting strain as a key control parameter.

Contribution

The paper reveals that strain, not valley coherence, dominates the linear polarization in moiré excitons, providing new insights into optical control in TMD superlattices.

Findings

Linear polarization correlates strongly with local strain and Raman shifts.

Strain amplifies C3 symmetry breaking, affecting emission polarization.

Strain is identified as the main factor influencing optical readout.

Abstract

Reliable optical control of valley degrees of freedom in moir\'e excitons requires that the emitted polarization faithfully reflect the underlying valley state. Here, we show that linearly polarized photoluminescence from WSe2/WS2 moir\'e excitons is largely insensitive to the excitation polarization and therefore does not arise from valley coherence. Automated polarization-resolved photoluminescence and Raman mapping at cryogenic temperature reveals that the degree of linear polarization correlates strongly with local Raman shifts and moir\'e-exciton observables, identifying strain as the dominant experimental correlate. Linear-regression analysis further shows that strain-related descriptors provide the best prediction of the observed polarization. Guided by theory, we attribute this behavior to strain-amplified breaking of C3 symmetry in the moir\'e potential: weak uniaxial strain produces only partial cancellation of locally elliptical emission, yielding a finite far-field degree of linear polarization. These results establish strain as a key control parameter for reliable optical readout in TMD moir\'e superlattices.