Josephson effect in copper oxide superconducting structures

Electron transport and microwave properties of copper oxide superconducting structures (bicrystal junctions and hybrid mesa-heterostructures) are discussed. Superconducting current in junctions from cuprate superconductors with the dominant dx2-y2-wave symmetry is determined by the barrier properties, characterized by the mid-gap bound states due to the multiple Andreev reflection. In bicrystal junctions it reveals via linear dependence of critical current density on square root of the transparency, and an increase of spectral density of shot noise at low voltages are observed. The experiments demonstrate that the superconducting hybrid mesa-heterostructures have the critical current density jc = 1-700 A/cm2 for an antiferromagnetic interlayer with thickness dM = 10-50 nm and the characteristic decay length of superconducting correlations of order of 7 nm, due to the anomalous longrange proximity effect, analyzed in the model of coupled superconductors via multilayer magnetic layer with antiferromagnetic ordering of magnetization in the layers. It is found that the hybrid mesa-heterostructures have much greater sensitivity to external magnetic field than conventional Josephson junctions because of the strong dependence of superconducting current on interlayer spin state.