Melting of the Abrikosov flux lattice in anisotropic superconductors

Abstract

It has been proposed that the Abrikosov flux lattice in high-${\mathit{T}}_{\mathit{c}}$ superconductors is melted over a significant fraction of the phase diagram. We provide a thermodynamic argument which establishes that the angular dependence of the melting temperature is controlled by the superconducting mass anisotropy. Using a low-frequency torsional-oscillator technique, this relationship has been tested in untwinned single-crystal ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$. The results offer decisive support for the melting proposal.