Exciton fine structure splitting and linearly polarized emission in strained transition-metal dichalcogenide monolayers

TL;DR

This paper theoretically investigates how anisotropic elastic strain affects exciton energy levels, optical properties, and fine structure in transition-metal dichalcogenide monolayers, revealing strain-induced polarization, splitting, and Dirac points.

Contribution

It provides a comprehensive microscopic theory and symmetry analysis of strain effects on exciton fine structure in atom-thin transition-metal dichalcogenides.

Findings

Strain breaks chiral selection rules, inducing linear polarization.

Elastic strain contributes additively to exciton fine structure splitting.

Strain can create Dirac points with linear dispersion in exciton spectrum.

Abstract

We study theoretically effects of an anisotropic elastic strain on the exciton energy spectrum fine structure and optical selection rules in atom-thin crystals based on transition-metal dichalcogenides. The presence of strain breaks the chiral selection rules at the $\bm K$-points of the Brillouin zone and makes optical transitions linearly polarized. The orientation of the induced linear polarization is related to the main axes of the strain tensor. Elastic strain provides an additive contribution to the exciton fine structure splitting in agreement with experimental evidence obtained from uniaxially strained WSe$_2$ monolayer. The applied strain also induces momentum-dependent Zeeman splitting. Depending on the strain orientation and magnitude, Dirac points with a linear dispersion can be formed in the exciton energy spectrum. We provide a symmetry analysis of the strain effects and develop a microscopic theory for all relevant strain-induced contributions to the exciton fine structure Hamiltonian.