TUNNELING OBSERVATION OF TL QUASI-LOCALIZED IMPURITY STATES IN SUPERCONDUCTIVE SEMICONDUCTOR PB(TL)TE

The superconductivity of Pb(Tl)Te has shown a possibility of strong co rrelation with the resonance scattering of carriers with quasi-localiz ed TI impurity states. In order to detect the quasi-localized states d irectly, tunneling spectrum observation was carried out with use of se veral planar and point-contact junctions on well-defined HWE film samp les. As a result, two quasi-localized Tl impurity states, QL1 and QL2 at an interval of 13-15 meV, were reproducibly observed on the spectra . Comparing these two states among the spectra observed on the samples with homogeneous Tl distribution, it is found that the upper QL1 stat e shows a half-width of Gamma(QL1) = 6+/-1 meV which is about a half o f Gamma(QL2) for the second QL2 state. This result means the occurrenc e of stronger resonance scattering with the QL1 state, and shows a deg ree of consistency with the electrical transport characteristics as ha d been reported [1]. A larger enhancement in superconducting T-c had a ctually been observed at the upper QL1 state rather than at the QL2 st ate. The obtained results strongly support the resonance scattering mo del for the superconductivity in this Pb(TI)Te system.