Nonlinear electrical phenomena and microwave detection in superconductor-normal metal contacts

Abstract

Energy gap peculiarities, excess current and non-monotonic temperature dependence of the first derivative of I-V curve of superconductor-normal metal contacts with immediate conductivity have been observed and investigated experimentally. It was clarified that formation of I-V curve non-linearity and its temperature evolution, in accordance with the microscopic theory 1, was associatted with existence of two mechanisms of charge transfer across S-N interface by quasiparticles: 1) with energy |E| > Δ; 2) with energy |E| > Δ, transferred from the N-in the S-region with conversion in the S-region in Cooper pairs. Investigation of microwave (λ = 8 mm) detection by S-N contacts enabled to observe additional response peak caused by energy gap peculiarity on I-V curve; at the same time the presence of this peculiarity permitted to realize maximum sensitivity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim 10^{4}</tex> V/W) to small ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim 10^{-9}</tex> ) microwave signal.