Direct spectroscopic evidence for mixed-valence Tl in the low carrier-density superconductor Pb${}_{1-x}$Tl${}_x$Te

P. Walmsley, C. Liu, A. D. Palczewski +4

Upon doping with Tl the narrow band-gap semiconductor PbTe exhibits anomalously high temperature superconductivity despite a very low carrier density as well as signatures of the K…