Exchange-split multiple Rydberg series of excitons in anisotropic quasi two-dimensional ReS$_{2}$

TL;DR

This study investigates excitonic Rydberg series in anisotropic ReS2 using polarization-resolved magnetoluminescence, revealing dark and bright excitons influenced by exchange interactions and magnetic fields, suggesting higher symmetry than crystal structure.

Contribution

It provides the first detailed analysis of multiple Rydberg exciton series in ReS2, highlighting exchange interactions and magnetic brightening effects in an anisotropic 2D material.

Findings

Two linearly polarized Rydberg exciton series observed.

Dark exciton series are brightened by in-plane magnetic field.

All exciton series extrapolate to the same bandgap, indicating a common origin.

Abstract

We perform a polarization-resolved magnetoluminescence study of excitons in ReS$_2$. We observe that two linearly polarized Rydberg series of excitons are accompanied by two other Rydberg series of dark excitons, brightened by an in-plane magnetic field. All series extrapolate to the same single-electron bandgap, indicating that the observed excitons originate either from the same valley or from two valleys related by the inversion symmetry, and are split by exchange interaction. To interpret our observations of the magnetic brightening, we have to assume the dominant spin-orbit coupling to be Ising-like, which hints at an approximate symmetry of the electronic states in ReS$_2$ which is higher than the crystal symmetry $C_i$.