ABSENCE OF A FINITE-TEMPERATURE VORTEX-GLASS PHASE-TRANSITION IN 2-DIMENSIONAL YBA2CU3O7-DELTA FILMS

Nonlinear current-voltage characteristics are investigated for the high-magnetic-field state of ultrathin (down to approximately 1 unit cell thick) YBa2Cu3O7-delta films. The current density where nonlinearity sets in, J(nl), exhibits a nontrivial power-law temperature dependence, J(nl) is-proportional-to T3.0+/-0.3, which quantitatively verifies a prediction from the vortex-glass theory for two dimensions (2D). Additionally, a critical scaling analysis of the I-V data clearly manifests the differences between a 2D and 3D vortex glass. The results suggest that a 2D vortex glass does not order at finite temperatures.