Rydberg series of dark excitons and the conduction band spin-orbit splitting in monolayer WSe2

Piotr Kapuściński,Alex Delhomme,Kenji Watanabe,Takashi Taniguchi,Marek Potemski,Magdalena Grzeszczyk,Miroslav Bartos,Diana Vaclavkova,Artur O Slobodeniuk,Clément Faugeras

doi:10.1038/s42005-021-00692-3

Abstract

Strong Coulomb correlations together with multi-valley electronic bands in the presence of spin-orbit interaction are at the heart of studies of the rich physics of excitons in monolayers of transition metal dichalcogenides (TMD). Those archetypes of two-dimensional systems promise a design of new optoelectronic devices. 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 tungsten diselenide monolayer, 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.

Highlights

Strong Coulomb correlations together with multi-valley electronic bands in the presence of spin-orbit interaction are at the heart of studies of the rich physics of excitons in monolayers of transition metal dichalcogenides (TMD)
All these studies have been largely focused on excitonic ground states, whereas the physics of dark excitons associated with the excited excitonic states is a little-explored area[20,21,22]
Note, that in the case of TMD monolayers, the jz = ±1 selection rules for optical transitions coincide with the ansatz of conservation of electronic spins in optical transitions

Summary

Introduction

Strong Coulomb correlations together with multi-valley electronic bands in the presence of spin-orbit interaction are at the heart of studies of the rich physics of excitons in monolayers of transition metal dichalcogenides (TMD). By comparing energy diagrams of dark and bright exciton series, we experimentally derive the single-particle separation between spin–orbit–split conduction band subbands in a WSe2 monolayer.

Results

Conclusion