Specific heat of single crystals of YBa2Cu3O7−δ: Fluctuation effects in a bulk superconductor

Abstract

Gaussian fluctuations have been observed in the specific heat of two single crystals ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. Deviations from a BCS-type step are well accounted for by 3D Gaussian fluctuations whose amplitude ratio, in the cleaner sample, implies that the number of order-parameter components is 7±2. This result is inconsistent with an O(2) Ginzburg-Landau theory.