Long-lived spin plasmons in a spin-polarized two-dimensional electron gas

TL;DR

This paper predicts the existence of long-lived spin plasmons in highly spin-polarized two-dimensional electron gases, which could enhance spintronic device performance and are observable via Raman scattering.

Contribution

It introduces the concept of long-lived spin plasmons in a spin-polarized 2D electron gas, a phenomenon not previously identified, under specific polarization conditions.

Findings

Long-lived spin plasmons exist for polarization P > 1/7.

Spin plasmons can be observed within a pseudo gap in the excitation spectrum.

Potential applications include improved coupling in spintronic devices.

Abstract

Collective charge-density modes (plasmons) of the clean two-dimensional unpolarized electron gas are stable, for momentum conservation prevents them from decaying into single-particle excitations. Collective spin-density modes (spin plasmons) possess no similar protection and rapidly decay by production of electron-hole pairs. Nevertheless, if the electron gas has a sufficiently high degree of spin polarization ($P>1/7$, where $P$ is the ratio of the equilibrium spin density and the total electron density, for a parabolic single-particle spectrum) we find that a long-lived spin-plasmon---a collective mode in which the densities of up and down spins oscillate with opposite phases---can exist within a "pseudo gap" of the single-particle excitation spectrum. The ensuing collectivization of the spin excitation spectrum is quite remarkable and should be directly visible in Raman scattering experiments. The predicted mode could dramatically improve the efficiency of coupling between spin-wave-generating devices, such as spin-torque oscillators.