Experimental Search For The Origin Of Low-Energy Modes In Topological Materials

Point-contact spectroscopy of several nonsuperconducting topological materials reveals a low-temperature phase transition that is characterized by a Bardeen-Cooper-Schrieffer type of criticality. We find such a behavior of differential conductance for topological surfaces of nonmagnetic and magnetic Pb1-y-xSnyMnxTe. We examine a possible contribution from superconducting nanoparticles, and show to what extent our data are consistent with Brzezicki's et al. theory (arXiv:1812.02168), assigning the observations to a collective state adjacent to atomic steps at topological surfaces.