Excitons and Optical Absorption on the Surface of a Strong Topological Insulator with a Magnetic Energy Gap

TL;DR

This paper theoretically investigates excitons and optical absorption on the magnetized surface of a strong topological insulator, revealing unique features influenced by magnetic fields and light polarization, with implications for experimental detection.

Contribution

It introduces a theoretical model predicting how magnetic exchange fields affect excitonic energy levels and optical absorption on TI surfaces, highlighting tunable and measurable effects.

Findings

Enhanced exciton binding energy with magnetic alignment

Optical absorption depends on magnetic field direction and light chirality

Tunable exciton center-of-mass motion via particle-hole asymmetry

Abstract

We present a theoretical study of interacting electron-hole pairs located on a magnetized surface of a strong topological insulator (TI). The excitonic energy levels and the optical absorption on such surface display unique and potentially measurable features such as (i) an enhanced binding energy for excitons whose total angular momentum is aligned with the magnetic exchange field, (ii) a stark dependence of the optical absorption on the direction of the magnetic exchange field as well as on the chirality of the incident light, and (iii) a tunable center-of-mass motion of spinful excitons induced by particle-hole asymmetry in the exchange field. Our predictions are relevant to surfaces of magnetically doped TIs or surfaces coated with magnetic films, in addition to TI nanowires placed under longitudinal magnetic fields.