Very thin YBa₂Cu₃O₇step-edge Josephson junctions

Step-edge Josephson junctions were fabricated from 20 and 10 nm thick epitaxial YBa 2 Cu 3 O 7 films on SrTiO 3 substrates. The junction cross sections were in the 10 -8 cm 2 range, similar to those in standard 200-300 nm thick junctions. The current-voltage characteristics, with and without microwave irradiation, were of resistively-shunted-junction (RSJ) type. The junction resistivities were in the range 10 -8 -10 -7 Omega cm 2 range, up to two orders of magnitude higher than in standard junctions, while the I c R n s were comparable. This behaviour was explained by a strong decrease in the number of parallel point-contact-type connections with the junction thickness. The junctions deteriorated quickly upon thermal cycling.