Superconductivity in amorphous Ta/Ge multilayers

Abstract

This paper reports measurements of the superconducting transition temperature (${\mathit{T}}_{\mathit{c}}$) of Ta/Ge multilayers for a range of individual layer thicknesses. Thick amorphous Ta layers which are isolated by thick insulating (Ge) layers have a transition at 0.9 K, and it is noted that for thinner isolated layers ${\mathit{T}}_{\mathit{c}}$ approaches zero as the resistance per square approaches the quantum resistance h/(2e${)}^{2}$. However, the transition temperature is enhanced in samples with thin Ge layers, and in films with Ta layers thinner than 1.5 nm ${\mathit{T}}_{\mathit{c}}$ rises to near 3 K. The enhancement is consistent with a proximity effect involving layers of a Ta-Ge alloy at the layer boundary. \textcopyright{} 1996 The American Physical Society.