Transition from activated to diffusive behavior in the vortex-liquid state in YBa2Cu3O7

Abstract In the vortex-liquid state in YBa 2 Cu 3 O 7 , there exist two distinct dissipative states separated by a field H > k . Below H k , the resistivity is strongly field-activated, with a prefactor that is anomalously enhanced over the normal-state resistivity ϱ N by ≈12 orders of magnitude. At H k , the prefactor collapses to a temperature-independent value equal to ϱ N , and the vortex motion becomes diffusive. The existence of the H k boundary is also reflected in the anomalous behavior of the Hall resistivity.