Latent heat and nonlinear vortex liquid in the vicinity of the first-order phase transitionin layered high-Tc superconductors

Abstract : In this work we revisit the vortex matter phase diagram in layered superconductors solving still open questions by means of ac and dc local magnetic measurements in the paradigmatic Bi2Sr2CaCu2O8 compound. We show that measuring with ac magnetic techniques is mandatory in order to probe the bulk response of vortex matter, particularly at high temperatures where surface barriers for vortex entrance dominate. From the TFOT evolution of the enthalpy and latent heat at the transition we find that, contrary to previous reports, the nature of the dominant interlayer coupling is electromagnetic in the whole temperature range. By studying the dynamic properties of the phase located at T TFOT, we reveal spanning in a considerable fraction of the phase diagram of a nonlinear vortex phase suggesting that bulk pinning might play a role even in the liquid vortex phase.