Tunable linear polarization of interface excitons at lateral heterojunctions

TL;DR

This paper presents a theory explaining how interface excitons at lateral heterojunctions in transition metal dichalcogenides exhibit tunable linear polarization in photoluminescence, influenced by microscopic mechanisms and external electric fields.

Contribution

It introduces a microscopic theory of polarized photoluminescence for interface excitons, highlighting mechanisms for linear polarization and its electrical tunability.

Findings

Linear polarization can exceed 10% in realistic heterostructures.

Wave-vector-dependent corrections modify optical selection rules.

External electric fields enable control over polarization direction and strength.

Abstract

We develop a theory of polarized photoluminescence of interface excitons localized at lateral heterojunctions between transition metal dichalcogenide monolayers. We show that the circular selection rules governing interband optical transitions exactly at the band extrema are modified at finite wave vectors. The corresponding wave-vector-dependent corrections to the optical matrix elements result in a net linear polarization of excitonic photoluminescence. We identify two microscopic mechanisms responsible for linear polarization$-$trigonal warping of the electron and hole dispersions and the energy dependence of the effective masses. Their interplay controls both the magnitude and the angle of the emitted light polarization, with distinct dependences on the crystallographic orientation of the interface. Using a microscopic variational approach, we demonstrate that the degree of linear polarization can reach values exceeding 10% in realistic heterostructures. Furthermore, due to the large built-in dipole moment of interface excitons, their optical response can be tuned by an external in-plane electric field, enabling control over the strength and direction of the polarization.