Soft-x-ray spectroscopy of monolayer transition metal dichalcogenides: valley selectivity?

TL;DR

This study uses theoretical and computational methods to explore valley selectivity in soft-x-ray transitions of monolayer transition metal dichalcogenides, revealing potential for valleytronic diagnostics and experimental applications.

Contribution

It predicts valley selectivity in x-ray transitions for specific edges using group theory and DFT, extending valley physics understanding beyond optical methods.

Findings

Valley selectivity predicted for s, p1/2, p3/2 edges with circular polarization.

Potential applications in valleytronics diagnostics and intervalley dynamics.

Feasibility of time-resolved x-ray experiments discussed.

Abstract

Optical properties of semiconducting monolayer transition metal dichalcogenides have received a lot of attention in recent years, following the discovery of the valley selective optical population of either $K_{+}$ or $ K_{-}$ valleys at the direct band gap, depending on the polarisation of the incoming light. We use group theoretical selection rules, as well as ab initio DFT calculations, to investigate whether this valence/conduction valley selectivity effect is also present in x-ray optical transitions from a core level of the metal atom to the valence and conduction band $K$ valleys. Valley selectivity is predicted for $s$, $p_{1/2}$ and $p_{3/2}$ edges in transitions to and from the valence band edges with circularly polarised radiation. Possible novel applications to the diagnostics of valleytronic properties and intervalley dynamics are investigated and the feasibility of time-resolved pump-probe and high resolution experiments with suitable soft-x-ray free-electron laser sources is discussed.