Superconductivity and Tl quasilocal states in semiconductor Pb(Tl)Te

Abstract

Narrow-gap semiconductor PbTe shows superconductivity (T _cmax } 1.4 K) by introduction of a small amount of Tl, and the superconductivity has been discussed in terms of the carrier's resonant scattering with the Tl virtual bound states. For observation of the Tl impurity state, tunneling spectroscopy was carried out on the Pb(Tl)Te films grown by the hot-wall epitaxial method (HWE), and succeeded in the detection of two quasilocal impurity levels. By another systematic studies using additional dopant Na into Pb(Tl)Te, it was also recognized that the superconductivity is remarkably enhanced when the fermi levelE _f encounters with these two impurity levels during the increase of the Na doping. These observed results indicate the superconducting property directly connected with the resonant scattering mechanism.