Specific Heat of YBa2Cu3O7: Origin of the "Linear" Term and Volume Fraction of Superconductivity

Abstract

Correlations of the coefficient of the "linear" term in the specific heat, $\gamma \mathrm{}\left(0\right)\mathrm{}$, and the discontinuity at $T_c$, $\Delta C\left(T_c\right)$, with a measured concentration of ${\mathrm{Cu}}^{2+}$ magnetic moments suggest the operation of a pairbreaking mechanism that limits the transition to the superconducting state and produces a contribution to $\gamma \mathrm{}\left(0\right)\mathrm{}$. There is no evidence for the existence of an intrinsic contribution to $\gamma \mathrm{}\left(0\right)\mathrm{}$. The value of $\Delta C\left(T_c\right)$ for a sample provides a measure of the volume fraction of superconductivity and a basis for correcting measured values of parameters to those characteristic of the fully superconducting state. Estimates of several quantities relevant to the strength of coupling are given.