Electrical Transport Properties of Josephson Junctions Using Polyimide Langmuir-Blodgett Films

Abstract

Using thermally stable ultrathin polyimide (PI) Langmuir-Blodgett films, we made tunnel junctions having structures of Nb/PI/(Pb–Bi) and Au/PI/(Pb–Bi). Then we examined the electrical transport properties of the junctions. Here, Nb and Pb-Bi are superconducting electrodes, and Au is a base-(noble metal) electrode. For Nb/PI/(Pb–Bi) junctions, it was found that an inherent oxide layer formed on a base-Nb electrode makes a significant contribution to the electrical conduction through the PI layer and that a typical current-voltage ( I - V ) characteristic based on the ideal Josephson junction was obtained even when the number of deposited PI layers was zero. For Au/PI/(Pb–Bi) junctions, typical I - V characteristics of tunnel junctions were obtained at a temperature below the critical temperature of a Pb–Bi superconducting alloy only when the number of deposited layers was 27.