Explanation of low critical currents in flat, bulk versus meandering, thin-film [001] tilt bicrystal grain boundaries inYBa2Cu3O7

Thin-film and bulk [001] tilt, bicrystal grain boundaries in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ exhibit a strong dependence of critical current density on misorientation angle. What is particularly difficult to understand is its thirty times lower magnitude in bulk grain boundaries which are microscopically more perfect, i.e., flatter, minimally faceted, and free of impurity phases. A plausible explanation, based on differences of the pinning of Josephson vortices in these grain boundary types, is proposed here.