Anomalous in-plane paraconductivity in single-crystal YBa2Cu3O7

Abstract
We have studied the in-plane paraconductivity in single crystals of YBa2 Cu3 O7 with exceptionally sharp transitions. For temperatures greater than ∼1 K above the transition temperature Tc, we find good qualitative and some quantitative agreement with the two-dimensional Aslamazov-Larkin theory. The jump to zero resistance occurs in a narrow interval of less than 0.5 K. Our data are inconsistent with the Lawrence-Doniach expression for crossover from two to three dimensions.