Investigation of electric field penetration into superconducting tantalum near a normal-superconducting interface

Abstract

The temperature dependence of the excess resistance of Ta-Cu-Ta sandwiches was investigated. The samples were prepared by the mutual rolling of the bulk materials, with the thickness of the superconducting plates (⋍0.1 cm) much greater than the penetration length of the electric field into the superconductorlE up to temperatures very close toTc. The penetration of the electric field through the clean NS interface into a superconductor with a relatively long electronic mean path (1⋍ξ0) was studied. We used an rf SQUID voltmeter to measure the resistance, ∼10−9 Ω, at currents not exceeding 1 mA. The experimental data were compared with the Artemenko-Volkov and Hsiang-Clarke theories. The electron-phonon relaxation time τɛ for our tantalum sample was estimated to be ∼1×10−10 sec.