# Larger than 80$\,$% Valley Polarization of Free Carriers in Singly-Oriented Single Layer WS$_2$ on Au(111)

## TL;DR

This study demonstrates that singly-oriented single layer WS₂ on Au(111) exhibits over 80% valley polarization of free holes at room temperature, with distinct electron and hole dynamics affecting polarization retention.

## Contribution

The paper provides the first direct measurement of high valley polarization in free carriers of WS₂ on Au(111) using time- and angle-resolved photoemission spectroscopy.

## Key findings

- Achieved 84% valley polarization for free holes at room temperature.
- Observed lower valley polarization for photoexcited electrons.
- Identified intervalley scattering into dark states as a key depolarization mechanism.

## Abstract

We employ time- and angle-resolved photoemission spectroscopy to study the spin- and valley-selective photoexcitation and dynamics of free carriers at the K and K' points in singly-oriented single layer WS$_2$/Au(111). Our results reveal that in the valence band maximum an ultimate valley polarization of free holes of 84$\,$% can be achieved upon excitation with circularly polarized light at room temperature. Notably, we observe a significantly smaller valley polarization for the photoexcited free electrons in the conduction band minimum. Clear differences in the carrier dynamics between electrons and holes imply intervalley scattering processes into dark states being responsible for the efficient depolarization of the excited electron population.