Topological spin-plasma waves

TL;DR

This paper explores how the unique spin-momentum locking in topological insulator surfaces enables topologically nontrivial hybrid spin-plasma modes that significantly influence thermal transport properties.

Contribution

It demonstrates the coupling of plasma and spin waves at topological insulator interfaces and reveals their topological nature and thermal Hall effects.

Findings

Coupling between plasma and spin waves at interfaces.

Topologically nontrivial hybrid modes.

Large thermal Hall response.

Abstract

The surface of a topological insulator hosts Dirac electronic states with the spin-momentum locking, which constrains spin orientation perpendicular to electron momentum. As a result, collective plasma excitations in the interacting Dirac liquid manifest themselves as coupled charge- and spin-waves. Here we demonstrate that the presence of the spin component enables effective coupling between plasma waves and spin waves at interfaces between the surface of a topological insulator and insulating magnet. Moreover, the helical nature of spin-momentum locking textures provides the phase winding in the coupling between the spin and plasma waves that makes the spectrum of hybridized spin-plasma modes to be topologically nontrivial. We also show that such topological modes lead to a large thermal Hall response.