Field-induced broadening of the resistive transition and two-dimensional nature of flux pinning in Y₂Ba₄Cu₈O₁₆films

Abstract

We report a unique dual nature of the magnetic-field-dependent resistive losses in epitaxial films of superconducting Y₂Ba₄Cu₈O₁₆. For excitation currents coplanar with the magnetic field, the losses are identical in the ohmic regime for both longitudinal and transverse field orientations. In the nonlinear current-voltage regime, the transverse field results in the lorentz-force-induced instability in the fluxline lattice and a higher dissipation. Comparison of the flux-pinning potential in Y₂Ba₄Cu₈O₁₆ deduced from the thermally activated nonlinear voltage with data on YBa₂Cu₃O₇ suggests an important role of the increased separation between Cu-O superconducting planes in Y₂Ba₄Cu₈O₁₆ in flux pinning.