Indium quasi-local level and superconductivity in GezSn1−zTe:In

Abstract

Starting with the idea that indium creates a narrow impurity band of quasi-local resonant states in the valence band of the SnTeGeTe system, we have noticed that superconductivity with Tc>0.4 K in these materials requires not only partial electron occupation of the resonant states pinning the Fermi level, but also the following additional condition: on the energy scale the band of resonant impurity states should overlap additional valence band states with a high density of states. An analysis of a correlation between the experimental data of the resistivity, the Hall concentration and superconducting properties was made for solid solutions of GezSn1−zTe:In (0 ⩽ z ⩽ 0.4; In: 5 and 16 at.%). It was found that the superconducting parameters (Tc, Hc2(0)) have a bell-shaped function of the Ge content, revealing a maximum near the edge of the heavy-hole valence band.