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

(submitted), (2021)

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

Andrey Geondzhian, Angel Rubio, Massimo Altarelli

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.

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Notes
We thank Kin-Fai Mak , Jie Shan and Claudio Masciovecchio for interesting discussions. This work was supported by the Cluster of Excellence `Advanced Imaging of Matter' (AIM), Grupos Consolidados (IT1249-19) and SFB925 "Light induced dynamics and control of correlated quantum systems. The Flatiron Institute is a division of the Simons Foundation. A.G. thank Dong Eon Kim and was supported by a National Research Foundation of Korea grant funded by the Ministry of Science and ICT No. 2016K1A4A4A01922028.

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