Electrodynamics of MnBi2Te4 intrinsic magnetic topological insulators

Abstract

We report on the electrodynamics of MnBi₂Te₄ thin films, an intrinsic magnetic topological material. We study its optical conductivity from terahertz (THz) to ultraviolet (UV) frequencies as a function of the film thickness, highlighting the presence of surface topological states superimposed on the bulk electrodynamics response. For the thinnest film, where the charge transport is dominated by Dirac surface states, we investigate the effect of the phase transition from the high-temperature topological protected state to the low-temperature magnetic (time-reversal broken) state by measuring the optical conductivity across the Néel temperature. At low temperatures, the breaking of the time reversal symmetry affects the optical conductivity, indicating that a magnetic-induced gap opens below T_N.

High quality thin films of the intrinsic magnetic topological insulator MnBi₂Te₄ were studied by means of optical spectroscopy in a broad spectral range from THz to UV. By analysing the optical conductivity at room temperature for different thickness, the presence of surface topological states superimposed to the bulk electrodynamics response was highlighted. For the thinnest film, where charge transport is dominated by the Dirac surface states, the interplay between the magnetic phase transition and the topological surface states was investigated. Crossing the Neèl temperature, the optical conductivity measurements indicate the opening of a magnetic gap at the Dirac node