Momentum-resolved linear dichroism in bilayer MoS$_2$

TL;DR

This study reveals a significant linear dichroism in bilayer MoS₂, an inversion-symmetric material, caused by intralayer effects leading to anisotropic optical excitations, challenging the expectation of optical isotropy.

Contribution

It demonstrates the existence of strong linear dichroism in bilayer MoS₂ and models its origin through semiconductor Bloch equations, highlighting intralayer effects in symmetric crystals.

Findings

Observed up to 42.4% linear dichroism in bilayer MoS₂

Dichroism arises from intralayer single-particle effects

Optical excitations show anisotropic momentum dependence

Abstract

Inversion-symmetric crystals are optically isotropic and thus naively not expected to show dichroism effects in optical absorption and photoemission processes. Here, we find a strong linear dichroism effect (up to 42.4%) in the conduction band of inversion-symmetric bilayer MoS$_2$, when measuring energy- and momentum-resolved snapshots of excited electrons by time- and angle-resolved photoemission spectroscopy. We model the polarization-dependent photoemission intensity in the transiently-populated conduction band using the semiconductor Bloch equations and show that the observed dichroism emerges from intralayer single-particle effects within the isotropic part of the dispersion. This leads to optical excitations with an anisotropic momentum-dependence in an otherwise inversion symmetric material.