Title: Thermodynamics of the vortex liquid in heavy-ion-irradiated superconductors
Abstract: It is shown that the large effect of heavy ion irradiation on the thermodynamical properties of the anisotropic superconductor ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ extends well into the superconducting fluctuation regime. The presence of the induced amorphous columnar defects shifts the specific-heat maximum at the normal-to-superconducting transition. This effect is similar to that recently put into evidence in cubic ${\mathrm{K}}_{x}{\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{BiO}}_{3}$ $(x\ensuremath{\simeq}0.35)$. In both compounds, vortex pinning manifests itself as a sharp angular dependence of the equilibrium torque. In ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$, pinning by the defects appears at the temperature ${T}_{{C}_{p}}^{max}$ of the specific-heat maximum, well above the magnetic irreversibility line ${T}_{irr}(H)$. In isotropic ${\mathrm{K}}_{x}{\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{BiO}}_{3}$, the onset of the pinning-related torque anomaly tracks the onset of the specific-heat anomaly and the irreversibility line. In ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$, fluctuations of the amplitude of the order parameter (and not vortex line wandering) are ultimately responsible for the vanishing of pinning. In ${\mathrm{K}}_{x}{\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{BiO}}_{3}$, vortex pinning disappears only at the superconducting-to-normal transition. The results indicate that in both compounds, the pinning energy at the ``Bose-glass'' transition is large with respect to the total free energy gain in the superconducting state. By implication, the mechanism of this latter transition should be reconsidered.