Absence of a finite-temperature vortex-glass phase transition in two-dimensional YBa2Cu3O7-δ films

Nonlinear current-voltage characteristics are investigated for the high-magnetic-field state of ultrathin (down to ∼1 unit cell thick) YBa2Cu3O7-δ films. The current density where nonlinearity sets in, Jnl, exhibits a nontrivial power-law temperature dependence, JnlT3.0±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. © 1992 The American Physical Society.