Microwave dynamics and electromagnetic properties of YBa 2Cu 3O 7 step-edge junctions on MgO substrates

Abstract

In this paper, we report the successful fabrication and current-voltage characteristics of the epitaxial c-axis YBa 2Cu 3O 7 step-edge junctions (SEJs) on MgO substrates. The junctions were fabricated by patterning the laser deposited YBa 2Cu 3O 7 thin films on MgO substrates with ionmilled steps. Integer Shapiro steps were observed in the current-voltage characteristics up to 1 THz under 72 GHz external microwave irradiation. Additional subharmonic Shapiro steps have also been found in some junctions with small step height and film thickness ratio, which may be explained by the inhomogeneous YBa 2Cu 3O 7 grain boundary interface formed at the edges of the substrate step. Self-induced electromagnetic resonance (Fiske mode) peaks have been observed in the current-voltage curves of the SEJs with large step height and film thickness ratios. The Swihart velocity and the effective shunting capacitance have been estimated to be 6.9 × 10 6 m s −1 and 55 fF μm −2 at 4.2 K, respectively, from the voltage of the observed Fiske resonance. The shunting capacitance obtained from the electromagnetic resonance compares well with that estimated from the McCumber constant β c .