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

Abstract

Nonlinear current-voltage characteristics are investigated for the high-magnetic-field state of ultrathin (down to \ensuremath{\sim}1 unit cell thick) ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ films. The current density where nonlinearity sets in, ${\mathit{J}}_{\mathrm{nl}}$, exhibits a nontrivial power-law temperature dependence, ${\mathit{J}}_{\mathrm{nl}}$\ensuremath{\propto}${\mathit{T}}^{3.0\ifmmode\pm\else\textpm\fi{}0.3}$, 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.