Valley Plasmonics in the Dichalcogenides

TL;DR

This paper investigates plasmonic excitations in dichalcogenides, especially MoS₂, revealing multiple plasmon bands influenced by doping, band structure, and spin-orbit coupling, with implications for understanding their collective modes.

Contribution

It provides a detailed ab initio analysis of plasmonic excitations in MoS₂, highlighting the effects of multi-orbital bands and spin-orbit coupling on collective modes and inter-valley scattering.

Findings

Multiple plasmon bands observed in MoS₂.

Long-range and short-range screening lead to different collective modes.

Spin-orbit coupling influences inter-valley scattering and mode gapping.

Abstract

The rich phenomenology of plasmonic excitations in the dichalcogenides is analyzed as a function of doping. The many-body polarization, the dielectric response function and electron energy loss spectra are calculated using an ab initio based model involving material-realistic Coulomb interactions, band structure and spin-orbit coupling. Focusing on the representative case of MoS$_2$, a plethora of plasmon bands are observed, originating from scattering processes within and between the conduction or valence band valleys. We discuss the resulting square-root and linear collective modes, arising from long-range versus short-range screening of the Coulomb potential. We show that the multi-orbital nature of the bands and spin-orbit coupling strongly affects inter-valley scattering processes by gapping certain two-particle modes at large momentum transfer.