Characterization of YBCO bicrystal grain-boundary Josephson junctions on ndgao3 substrate in terms of conventional superconductivity models

We have fabricated high quality grain-boundary bicrystal YBCO Josephson junctions on the NdGaO3 substrates. At the temperature T=77 K,the I –V characteristic can be explained by means of the conventional overdamped resistively shunted junction model comprising thermal noise.The deviations of the magnetic dependence of the Josephson critical current Ic from the usual Fraunhofer diffraction pattern can be described by a combination of a peaked-at-the-edges distribution of the critical current density and of the rounding of the I –V characteristic due to thermal fluctuations.The same measurements were done also at T =4.2 K,at low thermal noise conditions.The experimental magnetic field dependence Ic vs H was described by using a peaked-at-the-edges asymmetric profile,where the asymmetry depends on the applied magnetic field.The relation between our phenomenological model and advanced microscopical theory of grain-boundary bicrystal YBCO junction based on alternating 0 and PI- contacts is discussed.2002