Intrinsic circularly-polarized exciton emission in a twisted van-der-Waals heterostructure

TL;DR

This paper reports the discovery of intrinsic circularly polarized exciton emission in twisted van-der-Waals heterostructures, revealing a new polarization mechanism driven by emergent symmetry, observable without magnetic fields.

Contribution

It demonstrates a novel polarization effect in twisted heterostructures caused by emergent symmetry, expanding understanding of light-matter interactions in 2D materials.

Findings

Significant circular polarization of excitons at zero magnetic field

Polarization sensitive to applied magnetic field

Effect driven by emergent pyromagnetic symmetry

Abstract

The investigation of excitons in van-der-Waals heterostructures has led to profound insights into the interplay of crystal symmetries and fundamental effects of light-matter coupling. In particular, the polarization selection rules in undistorted, slightly twisted heterostructures of MoSe$_2$/WSe$_2$ were found to be connected with the Moir\'e superlattice. Here, we report the emergence of a significant degree of circular polarization of excitons in such a hetero-structure upon non-resonant driving with a linearly polarized laser. The effect is present at zero magnetic field, and sensibly reacts on perpendicularly applied magnetic field. The giant magnitude of polarization, which cannot be explained by conventional birefringence or optical activity of the twisted lattice, suggests a kinematic origin arising from an emergent pyromagnetic symmetry in our structure, which we exploit to gain insight into the microscopic processes of our device.