Experimental search for the origin of low-energy modes in topological materials

Abstract

Point-contact spectroscopy of several topological materials reveals a low-bias conductance peak with Bardeen-Cooper-Schrieffer criticality. However, no surface or bulk superconductivity accompanies these Andreev reflection type of spectra. Here, the authors show, by studying Ag/Pb${}_{1\ensuremath{-}x\ensuremath{-}y}$Sn${}_{y}$Mn${}_{x}$Te junctions, that the low-bias anomaly is immune to doping with paramagnetic or ferromagnetic Mn impurities. They assign the low-temperature phase either to superconducting nanoprecipitates, not however detected within their experimental resolution, or to a Su-Schrieffer-Heeger-type of states formed by correlation-driven instability of 1D topological flat bands residing at edges of surface terraces.