Intervalley mixing of interface excitons at lateral heterojunctions

TL;DR

This paper investigates how the low symmetry of armchair lateral heterojunctions in transition metal dichalcogenide monolayers causes valley mixing, affecting exciton properties and photoluminescence polarization.

Contribution

It introduces a model for valley mixing in armchair heterojunctions and explores its effects on exciton fine structure and polarization behavior.

Findings

Valley coupling strength estimated at ~0.2 eV·Å.

Linear polarization of exciton photoluminescence up to 1/3 degree.

In-plane magnetic field causes depolarization of PL.

Abstract

$\require{mediawiki-texvc}$ We demonstrate that the low symmetry of armchair lateral heterojunction between transition metal dichalcogenide monolayers allows for the mixing of $\mathbf{K}_+$ and $\mathbf{K}_-$ valleys. From the tight binding model we estimate the strength of the valley coupling to be of the order of $0.2$ eV$\cdot{\AA}$ for typical heteropairs. We show that the valley mixing gives rise to the in-plane $g$-factor of localized electrons leading to the spin precession in the in-plane magnetic field. We further study the effects of the valley mixing on the fine structure and dynamics of excitons at type-II lateral heterojunctions. We find that the interplay of the valley mixing and long-range exchange interaction leads to the linear polarization of exciton photoluminescence along the armchair heterojunction with the degree of polarization up to $1/3$ under unpolarized excitation. Application of the in-plane magnetic field of the order of 10$-$100 mT in any direction leads to the depolarization of the photoluminescence.