Collective excitations of Dirac electrons in a graphene layer with spin-orbit interaction

TL;DR

This paper investigates how spin-orbit interaction affects the Coulomb screening and excitation spectra in graphene, revealing new plasmon modes and significant changes in dielectric properties due to the opened band gap.

Contribution

It provides a detailed analysis of the impact of spin-orbit interaction on collective excitations and dielectric functions in graphene, a novel aspect in the study of Dirac electron systems.

Findings

Emergence of an undamped plasmon mode from inter-band electron-hole excitations.

Significant reshaping of the dielectric function due to the band gap.

Recovery of the Dirac gas collective excitation at high carrier densities or large wave vectors.

Abstract

Coulomb screening and excitation spectra of electrons in a graphene layer with spin-orbit interaction (SOI) is studied in the random phase approximation. The SOI opens a gap between the valence and conduction bands of the semi-metal Dirac system and reshapes the bottom and top of the bands. As a result, we have observed a dramatic change in the long-wavelength dielectric function of the system. An undamped plasmon mode emerges from the inter-band electron-hole excitation continuum edge and vanishes or merges with a Landau damped mode on the edge of the intra-band electron-hole continuum. The characteristic collective excitation of the Dirac gas is recovered in a system with high carrier density or for a large wave vector.