Unexplained Superconductivity in the Metallic-Semiconducting NbGe2-Ge System

Abstract

We have observed superconductivity to 16°K in mixtures of metallic Nb${\mathrm{Ge}}_2$ and semiconducting Ge, and we show that both constituents are necessary. We show that the superconductivity is associated with the Nb${\mathrm{Ge}}_2$, although by itself, it is not a superconductor above 2.5°K. Various explanations are considered.