Chiral surface and edge plasmons in ferromagnetic conductors

TL;DR

This paper investigates how Berry curvature in ferromagnetic conductors influences surface and edge plasmons, revealing direction-dependent frequencies and potential control mechanisms linking plasmonics with spintronics.

Contribution

It introduces the concept of surface Berry plasmons in ferromagnetic conductors and analyzes their unique directional properties caused by Berry curvature effects.

Findings

Edge plasmon frequency depends on propagation direction.

Berry curvature induces handedness in surface plasmons.

Control of plasmon propagation via magnetization is possible.

Abstract

The recently introduced concept of "surface Berry plasmons" is studied in the concrete instance of a ferromagnetic conductor in which the Berry curvature, generated by spin-orbit (SO) interaction, has opposite signs for carriers parallel or antiparallel to the magnetization. By using collisionless hy- drodynamic equations with appropriate boundary conditions, we study both the surface plasmons of a three-dimensional ferromagnetic conductor and the edge plasmons of a two-dimensional one. The anomalous velocity and the broken inversion symmetry at the surface or the edge of the conductor create a "handedness", whereby the plasmon frequency depends not only on the angle between the wave vector and the magnetization, but also on the direction of propagation along a given line. In particular, we find that the frequency of the edge plasmon depends on the direction of propagation along the edge. These Berry curvature effects are compared and contrasted with similar effects induced in the plasmon dispersion by an external magnetic field in the absence of Berry curvature. We argue that Berry curvature effects may be used to control the direction of propagation of the surface plasmons via coupling with the magnetization of ferromagnetic conductors, and thus create a link between plasmonics and spintronics.