Specific heat in the mixed state of superconductingYBa2Cu3O7−x

It is shown that the observed magnetic-field dependence of the specific-heat anomaly near the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ can be understood quantitatively by the Ginzburg-Landau theory of anisotropic type-II superconductors. It is shown, in the London limit, that the change in specific heat by the application of magnetic field ${\mathit{B}}_{\mathit{a}}$(∼1T) is approximately linear in (${\mathit{B}}_{\mathit{a}}$/${\mathit{T}}_{\mathit{c}}$)[t/(1-t)] for temperatures slightly below ${\mathit{T}}_{\mathit{c}}$, where t=T/${\mathit{T}}_{\mathit{c}}$. It is also predicted that the slope of this linear behavior for ${\mathbf{B}}_{\mathit{a}}$⊥c axis should be (${\mathit{m}}_{\mathit{c}}$/${\mathit{m}}_{\mathit{a}\mathit{b}}$ ${)}^{1/2}$ times lower than that for ${\mathbf{B}}_{\mathit{a}}$∥c axis. Here, ${\mathit{m}}_{\mathit{c}}$ and ${\mathit{m}}_{\mathit{a}\mathit{b}}$ are the components of the effective-mass tensor parallel and perpendicular to the c axis, respectively.