Mesoscopic conductance fluctuations in high-Tc grain boundary Josephson junctions: Coherent quasiparticle transport

Magneto-fluctuations of the normal resistance RN have been reproducibly observed in YBa2Cu3O7−δ (HTS) biepitaxial grain boundary junctions at low temperatures. We attribute them to mesoscopic transport in narrow channels across the grain boundary line. The Thouless energy appears to be the relevant energy scale. Possible implications on the understanding of coherent transport of quasiparticles in HTS and of the dissipation mechanisms are discussed.