Mesoscopic conductance fluctuations inYBa2Cu3O7−δgrain boundary junctions at low tem

Abstract

The magnetoconductance in YBa 2 Cu 3 O 7−␦ 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 20 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 K.

Macroscopic quantum phenomena in Josephson structures

“…Studies have been carried out at different voltages and non-equilibrium conditions. An energy scale of the order of 1 meV arises naturally from the analysis of the autocorrelation function of the conductance as a function of the voltage [59,60]. This has been identified as the Thouless energy C ε , and its value is consistent with a size of the channel of the order of 100 nm.…”

“…This is of relevance to investigate coherent quantum behavior in HTS [59,60]. Structural investigations allow first to locate macroscopic impurities which enclose the conducting channel, whose size is roughly confirmed by the period of the magnetic pattern of the critical current.…”

Electronic states and self-doping at a 45^o YBa2Cu3O7 grain boundary

“…Because substrate effects can be eliminated from transport measurements [16], such Josephson junctions are widely used to gain insight into the superconducting state (e.g., the properties and symmetry of the gap function, s-wave vs. d-wave) [15,17]. In addition, mesoscopic fluctuations of the magnetoconductance point to a coexistence of supercurrent and quasiparticle current [18].…”