Mesoscopic conductance fluctuations in YBa$_2$Cu$_3$O$_{7-\delta}$ grain boundary Junction at low temperature

TL;DR

This study investigates mesoscopic conductance fluctuations in YBCO grain boundary Josephson junctions at low temperatures, revealing coexistence of supercurrent and quasiparticle current even under high bias conditions.

Contribution

It demonstrates the persistence of mesoscopic fluctuations and supercurrent-quasiparticle coexistence at high voltages, supported by model calculations on quasiparticle relaxation.

Findings

Conductance fluctuations are mesoscopic in origin.

Supercurrent and quasiparticle current coexist at high bias.

Quasiparticle relaxation is reduced up to 3 Kelvin.

Abstract

The magneto-conductance in YBCO grain boundary Josephson junctions, displays fluctuations at low temperatures of mesoscopic origin. The morphology of the junction suggests that transport occurs in narrow channels across the grain boundary line, with a large Thouless energy. Nevertheless the measured fluctuation amplitude decreases quite slowly when increasing the voltage up to values about twenty times the Thouless energy, of the order of the nominal superconducting gap. Our findings show the coexistence of supercurrent and quasiparticle current in the junction conduction even at high nonequilibrium conditions. Model calculations confirm the reduced role of quasiparticle relaxation at temperatures up to 3 Kelvin.