Heat capacity of untwinned YBa2Cu3O7−δ crystals along the Hc2 line

Abstract

We report heat-capacity measurements on untwinned ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ single crystals in magnetic fields H≤7 T, for both H?c and H⊥c. Adding Gaussian fluctuations to a BCS-like step, we obtain a fit for H=0, T≊${\mathit{T}}_{\mathit{c}}$ that is consistent with a 3D, two-component order parameter in the strong-coupling limit. However, the H≠0 data are inconsistent with this approach. A finite-size-scaling analysis, assuming critical behavior and an H-dependent length, satisfactorily describes the data.