Superconductivity of (Sn1-zPbz)(1-x)In-x Te Alloys

The temperature dependences of the electrical resistivity of (Sn1-zPbz)(1-x )InxTe alloys with different concentrations of lead (z = 0-0.60) and indium (x = 0.03-0.20) were studied at temperatures T = 0.4-4.2 K in magnetic fie lds from zero to H = 15 kOe. A resistivity drop of no less than three-four orders of magnitude was observed in this range of alloy compositions. Appli cation of a magnetic field above a critical level resulted in a recovery of the sample resistivity to the original value. The observed resistivity dro p is identified with a superconducting transition. The critical parameters of the superconducting transition (T-c and H-c2) were determined at the dro p to one half the normal resistivity level. Experimental dependences of the critical superconducting-transition temperature T-c and of the second crit ical magnetic field H-c2 on the contents of lead (z) and indium (x) were me asured. The data obtained confirm a strong localization of the In impurity states and are evidence of the extrinsic nature of superconductivity in the class of materials under study. It was established that as the Pb content in (Sn1-zPbz)(1-x)InxTe increases, T-c and H-c2 decrease as the Fermi level E-F (fixed in the In impurity resonance band) leaves the Delta extremum an d the superconductivity breaks down when E-F leaves the L Sigma saddle poin t in the valence-band energy spectrum. (C) 2001 MAIK "Nauka/Interperiodica" .