Dimensionality crossover of the superconducting-normal transition in YBa₂Cu₃O_7-δ thin films both at high magnetic fields and at zero field

The IV characteristics of thin (250-4000 Å) YBa2Cu3O7-δ films show a crossover from the critical scaling behavior of the intrinsic three-dimensional (3D) transition, observed at high currents, to an ohmic resistance at low currents associated with a two-dimensional phase. This crossover is observed near the 3D phase transition from normal to vortex-glass phase in a high magnetic field, as well as for H = 0 near the transition into the Meissner phase. The crossover occurs when the growth of the 3D correlation length, ξθ(T - Tc,3D)-v, is limited by the film thickness. © 1991.