# Magnetic field control of light-induced spin accumulation in monolayer MoSe$_2$

## TL;DR

This study demonstrates how applying a magnetic field to monolayer MoSe2 can control light-induced spin accumulation in different valleys, revealing insights into ultrafast spin dynamics relevant for spintronics and valleytronics.

## Contribution

The paper introduces a magnetic field control method for spin accumulation in monolayer MoSe2 and provides a rate equation model explaining valley-specific spin-flip dynamics.

## Key findings

- Magnetic field influences spin accumulation in monolayer MoSe2.
- Spin relaxation rates differ between electrons and holes.
- Lifting valley degeneracy induces ultrafast spin-flip processes.

## Abstract

Semiconductor transition metal dichalcogenides (TMDs) have equivalent dynamics for their two spin/valley species. This arises from their energy-degenerated spin states, connected via time-reversal symmetry. When an out-of-plane magnetic field is applied, time-reversal symmetry is broken and the energies of the spin-polarized bands shift, resulting in different bandgaps and dynamics in the K$_+$ and K$_-$ valleys. Here, we use time-resolved Kerr rotation to study the magnetic field dependence of the spin dynamics in monolayer MoSe$_2$. We show that the magnetic field can control the light-induced spin accumulation of the two valley states, with a small effect on the recombination lifetimes. We unveil that the magnetic field-dependent spin accumulation is in agreement with hole spin dynamics at the longer timescales, indicating that the electron spins have faster relaxation rates. We propose a rate equation model that suggests that lifting the energy-degeneracy of the valleys induces an ultrafast spin-flip toward the stabilization of the valley with the higher valence band energy. Our results provide an experimental insight into the ultrafast charge and spin dynamics in TMDs and a way to control it, which will be useful for the development of new spintronic and valleytronic applications.