Flux Flow of Abrikosov-Josephson Vortices along Grain Boundaries in High-Temperature Superconductors

Low-angle grain boundaries (GBs) in superconductors exhibit intermediate Abrikosov vortices with Josephson cores, whose length l along GB is smaller than the London penetration depth, but larger than the coherence length. We found an exact solution for a periodic vortex structure moving along GBs in a magnetic field H and calculated the flux flow resistivity R_F(H), and the nonlinear voltage-current characteristics. The predicted R_F(H) dependence describes well our experimental data on 7° unirradiated and irradiated YBa₂Cu₃O₇ bicrystals, from which the core size l(T), and the intrinsic depairing density J_b(T) on nanoscales of a few GB dislocations were measured for the first time. The observed J_b(T) = J_b0(1-T/T_c)² indicates a significant order parameter suppression on GB.