Evidence for pinning of grain-boundary vortices by Abrikosov vortices in the grains of YBa2CU3O7

Data as a function of magnetic field on two types of bicrystal grain boudaries (GB's) of high-T-c superconductors show a peak in the critical current and an unusual inverse hysteresis. These results support a mechanism for an enhanced GB critical current, arising from interactions of GB vortices with pinned Abrikosov vortices in the banks of a GB, as suggested by Gurevich and Cooley. A substantial fraction of this enhancement (of order a factor of 2 after field cooling) also occurs upon exceeding the critical current of the grains after zero field cooling. A bulk GB and an isolated GB from a coated conductor show qualitatively identical results.