Coulomb excitations of monolayer germanene

TL;DR

This paper investigates the complex electronic excitations and plasmon modes in monolayer germanene, highlighting how spin-orbit coupling and buckled structure influence collective and single-particle behaviors under various conditions.

Contribution

It provides a detailed analysis of the unique plasmon modes in germanene, revealing their dependence on momentum, Fermi energy, and gate voltage, and compares them with silicene and graphene.

Findings

Four distinct plasmon modes identified.

Plasmons behave as 2D acoustic modes at long wavelengths.

Mode behaviors vary with momentum and electronic excitations.

Abstract

The feature-rich electronic excitations of monolayer germanene lie in the significant spin-orbital coupling and the buckled structure. The collective and single- particle excitations are diversified by the magnitude and direction of transferred momentum, the Fermi energy and the gate voltage. There are four kinds of plasmon modes, according to the unique frequency- and momentum-dependent phase diagrams. They behave as two-dimensional acoustic modes at long wavelength. However, for the larger momenta, they might change into another kind of undamped plasmons, become the seriously suppressed modes in the heavy intraband e-h excitations, keep the same undamped plasmons, or decline and then vanish in the strong interband e-h excitations. Germanene, silicene and graphene are quite different from one another in the main features of the diverse plasmon modes.