Rydberg series of dark excitons and the conduction band spin-orbit splitting in monolayer WSe$_2$

TL;DR

This paper reports the observation of Rydberg dark exciton series in monolayer WSe₂ and introduces a method to measure the conduction band spin-orbit splitting using these excitons.

Contribution

Demonstrates the existence of dark Rydberg excitons in monolayer WSe₂ and proposes a new experimental approach to determine conduction band spin-orbit splitting.

Findings

Observation of dark Rydberg excitons in WSe₂.

Comparison of bright and dark exciton energy ladders.

Method to evaluate conduction band spin-orbit splitting.

Abstract

Strong Coulomb correlations together with multi-valley electronic bands in the presence of spin-orbit interaction and possible new optoelectronic applications are at the heart of studies of the rich physics of excitons in semiconductor structures made of monolayers of transition metal dichalcogenides (TMD). In intrinsic TMD monolayers the basic, intravalley excitons are formed by a hole from the top of the valence band and an electron either from the lower or upper spin-orbit-split conduction band subbands: one of these excitons is optically active, the second one is "dark", although possibly observed under special conditions. Here we demonstrate the s-series of Rydberg dark exciton states in monolayer WSe$_2$, which appears in addition to a conventional bright exciton series in photoluminescence spectra measured in high in-plane magnetic fields. The comparison of energy ladders of bright and dark Rydberg excitons is shown to be a method to experimentally evaluate one of the missing band parameters in TMD monolayers: the amplitude of the spin-orbit splitting of the conduction band.