First-order transition and critical end point in vortex liquids in layered superconductors

We calculate various thermodynamic quantities of vortex liquids in a layered superconductor by using the nonperturbative parquet-approximation method, which was previously used to study the effect of thermal fluctuations in two-dimensional vortex systems. We find there is a first-order transition between two vortex liquid phases that differ in the magnitude of their correlation lengths. As the coupling between the layers increases, the first-order transition line ends at a critical point. We discuss the possible relation between this critical end point and the disappearance of the first-order transition that is observed in experiments on high-temperature superconductors at low magnetic fields.