Use of RF SQUID for electrical resistance measurements up to 30 K with high temperature superconductor wiring

Abstract

Using a high temperature superconductor (HTSC) as part of the wiring circuit, measurements of electrical resistivity were made up to 30 K with a high resolution bridge, using a direct current comparator and a RF SQUID as a null detector. The resolution achieved for resistances of 1 μω in which a 100 mA current was flowing was 10 −6 and 10 −4 at 4.2 and 30K, respectively. Advantage was taken of the bad thermal conductance of the HTSC to thermally decouple the sample, whose temperature ranged from 1.2 to 30 K, from the comparison resistance kept at 4.2K. The temperature gradient in the HTSC was ≈20 Kcm −1. This constitutes an application of HTSC in an electrical circuit in which no high density current flows.