Electron transport in high- Tc superconducting grain boundary junctions

Abstract

The current state and the prospects of the application of high- T c superconducting grain boundary Josephson junctions in microwave electronics devices are given. It is approached by sketching the typical fabrication technique of the junction. Josephson bicrystal junctions on sapphire substrate are considered in detail. The results of dc microwave and magnetic measurements of YBCO bicrystal junctions on r-cut sapphire are presented. The junctions with high resistance 10–20 Ω and I c R N=1–2 mV and tolerance of R N S around 30% on the chip allow to create microwave circuits with low integration (up to 10 junctions on chip). The microwave dynamics of the junction with superconducting current-phase relation fits with sin ϕ relation better than 5%, that clearly indicates the tunnel conductivity between two YBCO electrodes. It was found that critical current density depends on the square root of interface transparency in accordance with the prediction of superconducting current transport via Andreev's bound surface states. The specific properties of current transport in high- T c grain boundary junctions with taking into account d-wave type of gap order in high- T c superconductor are discussed.