Observations of the a.c. Josephson Effect in High- T c YBaCuO Point Contacts

Abstract

We have observed r.f.-induced Josephson steps using 70 GHz radiation in point contacts comprised of samples of YBaCuO which had a T_c ~ 80 K. Low junction resistances (~ 100 Ω) produced d.c. supercurrents of (2÷5) μA. At a temperature of 4.2 K, r.f.-induced steps up to n = 5 in YBaCuO/YBaCuO point contacts and up to n = 8 in NbZr/YBaCuO point contacts corresponding to a Josephson frequency of 350 GHz and 560 GHz, respectively, were observed. Step separation and step height dependence on the r.f. level were in agreement with ordinary Josephson tunnelling behaviour. These results imply singlet-state pairing of the electrons in the new superconducting materials.