The Origin of Linearly-Polarized Photoluminescence in WS2/WSe2 Moiré superlattices

Original Abstract

Reliable optical control of valley degrees of freedom in moire excitons requires that the emitted polarization faithfully reflect the underlying valley state. Here, we show that linearly polarized photoluminescence from WS2/WSe2 moiré excitons is largely insensitive to the excitation polarization and therefore is not primarily governed by valley-contrast selection rules. Automated polarization-resolved photoluminescence and Raman mapping at cryogenic temperatures reveal that the degree of linear polarization correlates strongly with local Raman shifts and moiré-exciton observables, identifying strain as the dominant experimental correlate. Exhaustive 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 moire 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 moire superlattices.