Anti-site defect-induced disorder in compensated topological magnet MnBi_2-xSb_xTe₄

MnBi_2-xSb_xTe₄ (MBST) was identified as an intrinsic magnetic topological insulator that exhibits exotic quantum phenomena such as quantum anomalous Hall effect and axion insulating state. However, atomic defects undermine the stabilization of such quantum phases as they lead to spatial variations in the surface state gap and doping levels. The large number of possible defect configurations in MBST further complicates the study on the influence of individual defects. Here, we present a statistical analysis of the nanoscale effect of defects in MBST with x = 0.64, by scanning tunnelling microscopy/spectroscopy [1]. We identify (Bi,Sb)_Mn anti-site defects to be the main source of the observed doping fluctuations, leading to the formation of nanoscale charge puddles and effectively closing the transport gap. Our findings will guide further optimization of this material system via defect engineering, to enable exploitation of its promising properties.