Infrared study of the layered, magnetic insulator Mn(Bi$_{0.07}$Sb$_{0.93}$)$_2$Te$_4$ at low temperatures

TL;DR

This study uses infrared spectroscopy to explore how magnetic ordering influences the electronic structure of a heavily Sb-doped topological insulator, revealing coupling effects at low temperatures.

Contribution

It provides the first detailed infrared analysis of magnetic and electronic coupling in Mn(Bi$_{0.07}$Sb$_{0.93}$)$_2$Te$_4$, highlighting temperature-dependent optical anomalies.

Findings

Anomalies in optical response across Neel temperature

Evidence of coupling between magnetic order and electronic structure

Temperature-dependent reflectivity changes observed

Abstract

Topological insulators with intrinsic magnetic ordering, potentially hosting rare quantum effects, recently attracted extensive attention. MnBi$_2$Te$_4$ is the first established example. The Sb-doped variant Mn(Bi$_{1-x}$Sb$_x$)$_2$Te$_4$ shows a great variety of electronic properties depending on the Sb content~$x$, such as shifts in the Fermi level and the Neel temperature $T_{\mathrm N}$, and the change of the free charge carrier type from $n$- to $p$-type at high Sb substitution ratios. Here, we investigate the effect of magnetic ordering on the bulk electronic structure of Mn(Bi$_{1-x}$Sb$_x$)$_2$Te$_4$ with high Sb content $x=0.93$ by temperature-dependent reflectivity measurements over a broad frequency range. We observe anomalies in the optical response across $T_{\mathrm N}$ when the antiferromagnetic order sets, which suggests a coupling between the magnetic ordering and the electronic structure of the material.