# Probing and manipulating valley coherence of dark excitons in monolayer WSe$_2$

## TL;DR

This study demonstrates how magnetic fields and exchange interactions can be used to probe and control the valley coherence of dark excitons in monolayer WSe2, advancing understanding of their quantum properties.

## Contribution

It introduces a method to manipulate valley coherence of dark excitons in WSe2 using polarization-resolved photoluminescence and magnetic fields.

## Key findings

- Magnetic fields enable probing valley coherence.
- Exchange interaction influences dark exciton properties.
- Valley degree of freedom can be manipulated externally.

## Abstract

Monolayers of semiconducting transition metal dichalcogenides are two-dimensional direct-gap systems which host tightly-bound excitons with an internal degree of freedom corresponding to the valley of the constituting carriers. Strong spin-orbit interaction and the resulting ordering of the spin-split subbands in the valence and conduction bands makes the lowest-lying excitons in WX$_2$ (X~being S or Se) spin-forbidden and optically dark. With polarization-resolved photoluminescence experiments performed on a WSe$_2$ monolayer encapsulated in a hexagonal boron nitride, we show how the intrinsic exchange interaction in combination with the applied in-plane and/or out-of-plane magnetic fields enables one to probe and manipulate the valley degree of freedom of the dark excitons.