Brightening of dark excitons in monolayers of semiconducting transition metal dichalcogenides

TL;DR

This study uses low temperature magneto-photoluminescence to show how in-plane magnetic fields can brighten dark excitons in monolayers of certain transition metal dichalcogenides, revealing material-specific behaviors and energy splittings.

Contribution

It demonstrates the magnetic brightening of dark excitons in monolayer TMDs and characterizes their energy splittings, providing new insights into excitonic properties under magnetic fields.

Findings

Dark excitons are brightened by in-plane magnetic fields in WSe₂ and WS₂ monolayers.

Dark exciton emission appears at ~50 meV below bright excitons with intensity growing as B².

MoS₂ monolayer has a dark exciton ground state with ~100 meV splitting.

Abstract

We present low temperature magneto-photoluminescence experiments which demonstrate the brightening of dark excitons by an in-plane magnetic field $B$ applied to monolayers of different semiconducting transition metal dichalcogenides. For both WSe$_2$ and WS$_2$ monolayers, the dark exciton emission is observed at $\sim$50 meV below the bright exciton peak and displays a characteristic doublet structure which intensity is growing with $B^2$, while no magnetic field induced emission peaks appear for MoSe$_2$ monolayer. Our experiments also show that the MoS$_2$ monolayer has a dark exciton ground state with a dark-bright exciton splitting energy of $\sim$100 meV.