fcc Metallic superconducting phase observed in vapor-quenched Se and Te films

Abstract

Microcrystalline Se and Te overgrowths having an abnormal A-1-type structure were quench-condensed at 4.2 K on fine-grained base films ofO ⁵ _h space group oxides vapor-quenched at the same temperature on suitable glass substrates. From measurements of the electrical resistance we found that in this metastable fcc phase Se and Te behave as metals and may become superconductors. On heating, one reaches a critical temperature at which the overgrowth breaks because of the increase in volume occurring when the metallic phase transforms to the less dense, ordinary A-8-type semiconducting structure. An analysis of the data shows that the smaller is the lattice constant of the base film oxide, the higher are the density, the bulk superconducting transition temperature, and the bulk conductivity of the metallic Se and Te and the lower is the breaking temperature of the overgrowth.