Thermodynamics of the vortex liquid in heavy ion-irradiated superconductors

Cornelis J. van der Beek; Marcin Konczykowski; Luc Fruchter; René Brusetti; Thierry Klein; Jacques Marcus; Christophe Marcenat

doi:10.1103/PhysRevB.72.214504

paper

Thermodynamics of the vortex liquid in heavy ion-irradiated superconductors

arXiv:cond-mat/0504100 · doi:10.1103/PhysRevB.72.214504

Abstract

It is shown that the large effect of heavy ion-irradiation on the thermodynamical properties of the anisotropic superconductor YBa $_{2}$ Cu $_{3}$ O $_{7 - δ}$ 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 K $_{x}$ Ba $_{1 - x}$ BiO $_{3}$ ( $x ≃ 0.35$ ). In both compounds, vortex pinning manifests itself as a sharp angular dependence of the \em equilibrium \rm torque. In YBa $_{2}$ Cu $_{3}$ O $_{7 - δ}$ , pinning by the defects appears at the temperature $T_{C_{p}}^{ma x}$ of the specific heat maximum, well above the magnetic irreversibility line $T_{i r r} (H)$ . In isotropic K $_{x}$ Ba $_{1 - x}$ BiO $_{3}$ , the onset of the pinning-related torque anomaly tracks the onset of the specific heat anomaly and the irreversibility line. In YBa $_{2}$ Cu $_{3}$ O $_{7 - δ}$ , fluctuations of the amplitude of the order parameter (and not vortex line wandering) are ultimately responsible for the vanishing of pinning. In K $_{x}$ Ba $_{1 - x}$ 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.

9 pages, 9 figures, resubmitted to PRB 23-09-2005