Supercurrent density correlation function of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// grain boundary Josephson junctions

We have measured the thermal noise induced slope R/sub p/(B) of the current-voltage characteristics of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// Grain Boundary Josephson Junctions (GBJs) for I/spl rarr/0 in magnetic fields up to B=12 T. From the measured R/sub p/(B) dependences the magnetic field dependence of the critical current I/sub c/(B) was derived in the large magnetic field range between 0 and 12 T. Finally, the supercurrent density correlation function was obtained from the I/sub c/(B) dependence using the Wiener-Khinchine relation. By introducing the concept of the bright (BGCF) and dark ground correlation function (DGCF) a spatial filtering of the information on the supercurrent density distribution was obtained. The investigation of the BGCFs and the comparison to DGCFs gives clear evidence that supercurrent density has strong inhomogeneities on small length scales in the nanometer regime.<>