Superconducting transition temperature of niobium/graphite bilayers

Abstract

The superconducting proximity effect in niobium/graphite bilayers was studied. Thin graphite films of various thickness ranging from around 20-160 nm were prepared by cleaving a kish graphite (KG). For making a specimen, niobium (Nb) of 40 nm in thickness was deposited on a KG film and a quartz glass substrate simultaneously using electron-beam evaporation method. Each resistance of Nb and Nb/KG films was measured at the same time, and transition temperature of Nb film (TSC) and Nb/KG film (T* C) on the same substrate was obtained. The ratio of T* C to TSC (T*C/T SC) showed a periodic characteristic with KG film thickness. Furthermore, the peak values of the ratio exceeded 1.00. This result suggests that the electron correlation at Nb/KG interface changes depending on KG film thickness because of the interference of electrons as wave in the KG film. © 2004 Elsevier B.V. All rights reserved.