Critical Current Density Distribution and Magnetic Flux States in YBa2Cu3O7_δ Bicrystal Grain Boundary Josephson Junctions

We have studied the spatial homogeneity of the critical current density Jc and static magnetic flux states in YBa2CusOτ-6 bicrystal grain boundary Josephson junctions (GBJs) using Low Temperature Scanning Electron Microscopy (LTSEM). By LTSEM the Jc distribution and the static magnetic flux states in the GBJs could be imaged with a resolution of less than 1/µm. Varying the applied magnetic field B the different magnetic flux states with up to more than 15 vortices in the GBJ could be observed. The spatial variation of the measured LTSEM voltage signal agrees well with the theoretically expected signal according to the sinusoidal modulation of the maximum Josephson current density by an external magnetic field. The LTSEM analysis clearly demonstrates that the spatial variation of Jc along the grain boundary is less than about 30% on the length scale of the spatial resolution of the LTSEM technique.