Spin and valley polarization of plasmons in silicene due to external fields

TL;DR

This paper explores how external electric and magnetic fields influence the spin and valley polarization of plasmons in silicene, revealing potential for spin- and valley-polarized plasmonic applications.

Contribution

It provides analytical and numerical analysis of plasmon dispersion, lifetime, and oscillator strength in silicene under combined electric and magnetic fields, highlighting spin and valley polarization effects.

Findings

Fields induce spin and valley textures in excitation spectrum

Spin polarization occurs when Fermi level is in a spin gap

Plasmon lifetime and strength depend on electron-hole pair composition

Abstract

The electronic properties of the novel two dimensional (2D) material silicene are strongly influenced by the application of a perpendicular electric field $E_z$ and of an exchange field $M$ due to adatoms positioned on the surface or a ferromagnetic substrate. Within the random phase approximation, we investigate how electron-electron interactions are affected by these fields and present analytical and numerical results for the dispersion of plasmons, their lifetime, and their oscillator strength. We find that the combination of the fields $E_z$ and $M$ brings a spin and valley texture to the particle-hole excitation spectrum and allows the formation of spin- and valley-polarized plasmons. When the Fermi level lies in the gap of one spin in one valley, the intraband region of the corresponding spectrum disappears. For zero $E_z$ and finite $M$ the spin symmetry is broken and spin polarization is possible. The lifetime and oscillator strength of the plasmons are shown to depend strongly on the number of spin and valley type electrons that form the electron-hole pairs.