Josephson effects and quantum interference in high-TC superconductors

Experiments have given evidence that the Ginzburg-Landau theory applies to high-TC superconductors; the coherence length, however, is considerably shorter than for conventional superconductors, viz., it is of the order of tenths of nm, which is comparable with the lattice parameters. As a consequence, planar defects in crystals such as grain boundaries or domain boundaries are a hindrance to the superconductor current. Thus, polycrystalline ceramic samples as well as single crystals do not behave as homogeneous materials; instead, they behave as systems of superconducting granules mutually bonded by weak Josephson junctions. These phenomena are demonstrated on an YBa2Cu3CO7 single crystal. Measurements of magnetization curves in a weak magnetic field using a SQUID magnetometer were useful in examinating the Josephson environment. Observation of the individual Josephson junctions inside the ceramics was accomplished on tip contacts. (Z.S.). 5 refs