Intrinsic Damping of Collective Spin Modes in a Two-Dimensional Fermi Liquid with Spin-Orbit Coupling

TL;DR

This paper demonstrates that collective spin modes in a two-dimensional Fermi liquid with spin-orbit coupling are intrinsically damped by electron-electron interactions, even at zero wavevector, due to non-conservation of total spin.

Contribution

It reveals the intrinsic damping mechanism of collective spin modes in 2D Fermi liquids with SOC, highlighting a fundamental difference from systems without SOC.

Findings

Damping occurs even at zero wavevector (q=0).

Linewidth scales with the square of the spin-orbit energy splitting.

Total spin is not conserved in the presence of SOC.

Abstract

A Fermi liquid with spin-orbit coupling (SOC) is expected to support a new kind of collective modes: oscillations of magnetization in the absence of the magnetic field. We show that these modes are damped by the electron-electron interaction even in the limit of an infinitely long wavelength (q = 0). The linewidth of the collective mode is on the order of {\Delta}^2=E_F , where {\Delta} is a characteristic spin-orbit energy splitting and E_F is the Fermi energy. Such damping is in a stark contrast to known damping mechanisms of both charge and spin collective modes in the absence of SOC, all of which disappear at q = 0, and arises because none of the components of total spin is conserved in the presence of SOC.