Anomalous light cones and valley optical selection rules of interlayer excitons in twisted heterobilayers

TL;DR

This paper reveals that twisted heterobilayers of transition metal dichalcogenides exhibit six-fold degenerate interlayer exciton light cones at finite velocities, enabling novel valley optical control and valley Hall effects.

Contribution

It uncovers the existence of anomalous finite-velocity light cones in twisted heterobilayers and their implications for valleytronics and exciton dynamics.

Findings

Interlayer excitons have six-fold degenerate light cones at finite velocities.

Photon emissions are elliptically polarized with helicity linked to valley indices.

Finite-velocity light cones enable optical valley polarization and valley current injection.

Abstract

We show that, because of the inevitable twist and lattice mismatch in heterobilayers of transition metal dichalcogenides, interlayer excitons have six-fold degenerate light cones anomalously located at finite velocities on the parabolic energy dispersion. The photon emissions at each light cone are elliptically polarized, with major axis locked to the direction of exciton velocity, and helicity specified by the valley indices of the electron and the hole. These finite-velocity light cones allow unprecedented possibilities to optically inject valley polarization and valley current, and the observation of both direct and inverse valley Hall effects, by exciting interlayer excitons. Our findings suggest potential excitonic circuits with valley functionalities, and unique opportunities to study exciton dynamics and condensation phenomena in semiconducting 2D heterostructures.