ANALYSIS OF THE CRITICAL-CURRENT DENSITY IN GRAIN-BOUNDARY JOSEPHSON-JUNCTIONS ON A NANOMETER-SCALE

The critical current Ic of YBa2Cu3O7-δ bicrystal grain boundary Josephson junctions GBJs) have been measured in igh magnetic fields up to B=12 T. Even at the highest applied magnetic fields, Ic varied periodically with varying magnetic field. By comparing the envelope of the measured Ic(B) dependencies to model calculations we obtain information on the spatial distribution of the supercurrent density jc on a length scale down to below 1 nm. Our analysis gives clear evidence that jc has spatial inhomogeneities on all length scales down to 1 nm with a probability distribution p(a) for the characteristic length scale a of the inhomogeneities.© 1995 American Institute of Physics.