Very thin YBa2Cu3O7 step-edge Josephson junctions

Step-edge Josephson junctions were fabricated from 20 and 10 nm thick epitaxial YBa2Cu3O7 films on SrTiO3 substrates. The junction cross sections were in the 10-8 cm2 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 cm2 range, up to two orders of magnitude higher than in standard junctions, while the IcRns 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.