Finite-size effects on the vortex-glass transition in thin YBa2Cu3O7- films

Abstract

Nonlinear current-voltage characteristics have been measured at high magnetic fields in YBa2Cu3O7- films of a thickness t ranging from 3000 down to 16. Critical-scaling analyses of the data for the thinner films (t 400) reveal deviations from the vortex-glass critical scaling appropriate for three-dimensional (3D) systems. This is argued to be a finite-size effect. At large current densities J, the vortices are probed at length scales smaller than the film thickness, i.e., 3D vortex-glass behavior is observed. At low J by contrast, the vortex excitations involve typical length scales exceeding the film thickness, resulting in 2D behavior. Further evidence for this picture is found directly from the 3D vortex-glass correlation length, which, upon approach of the glass transition temperature, appears to level off at the film thickness. The results indicate that a vortex-glass phase transition does occur at finite temperature in 3D systems, but not in 2D systems. In the latter an onset of 2D correlations occurs towards zero temperature. This is demonstrated in our thinnest film (16), which, in a magnetic field, displays a 2D vortex-glass correlation length which critically diverges at zero temperature. © 1995 The American Physical Society.