Infrared study of the layered magnetic insulator Mn(Bi0.07Sb0.93)2Te4 at low temperatures

Topological insulators with intrinsic magnetic ordering, potentially hosting rare quantum effects, recently attracted extensive attention. MnBi2Te4 is the first established example. The Sb-doped variant Mn(Bi1-xSbx)2Te4 shows a great variety of electronic properties depending on the Sb content x, such as shifts in the Fermi level and the Néel temperature TN, 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(Bi1-xSbx)2Te4 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 TN when the antiferromagnetic order sets, which suggests a coupling between the magnetic ordering and the electronic structure of the material.