Pjm. Woltgens et al., 2D-3D CROSSOVER EFFECTS ON THE VORTEX-GLASS PHASE-TRANSITION IN THIN YBA2CU3O7-DELTA FILMS, Physica. B, Condensed matter, 194, 1994, pp. 1911-1912
Nonlinear current-voltage characteristics have been measured for ultra
thin (16-400 angstrom) YBa2Cu3O7-delta films in high magnetic fields.
A scaling analysis of these data reveals deviations from the universal
vortex-glass critical scaling behavior observed for thick films. This
is argued to be a dimensionality effect: At large currents, one probe
s length scales smaller than the film thickness, i.e., the three-dimen
sional (3d) vortex-glass behavior, whereas at low currents the vortex
excitations involve typical length scales which exceed the film thickn
ess, hence the 2d behavior is exhibited. Further evidence for this pic
ture is found from the 3d vortex-glass correlation length, which appea
rs to be cut off by the film thickness.