Plasmon modes in the magnetically doped Single Layer and Multilayers of Helical Metals

TL;DR

This paper investigates plasmon excitations and electromagnetic responses in magnetically doped helical metals, revealing unique spin-plasmon modes and optical phenomena relevant for topological insulator surface states.

Contribution

It introduces the concept of spin-plasmon modes in magnetically doped helical metals and analyzes their electromagnetic responses in single and multilayer configurations.

Findings

Discovery of a spin-plasmon mode with rotating spin texture.

Observation of Faraday rotation due to plasmon excitations.

Identification of an additional optical mode within the plasmon gap.

Abstract

We study the plasmon excitations and the electromagnetic response of the magnetically doped single layer and multilayer of ``helical metals'', which emerge at the surfaces of topological insulators. For the single layer case, we find a ``spin-plasmon'' mode with the rotating spin texture due to the combination of the spin-momentum locking of ``helical metals'' and the Hall response from magnetization. For the multilayers case, we investigate the electromagnetic response due to the plasmon excitations, including the Faraday rotation for the light propagating normal to the helical metal layers and an additional optical mode with the frequency within the conventional plasmon gap for the light propagating along the helical metal layers.