Angular dependence of the latent heat of vortex-lattice melting in untwinnedYBa2Cu3O7−δ

Abstract

We measured the latent heat of vortex-lattice melting for varying angles \ensuremath{\Theta} between the external magnetic field H and the c axis of an untwinned ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ single crystal. The discontinuity in entropy at melting, $\ensuremath{\Delta}S$ per unit volume of sample, depends solely on the temperature T where melting occurs, but does not depend on \ensuremath{\Theta} and the corresponding melting field ${H}_{m}(T,\ensuremath{\Theta}).$ The T dependence of $\ensuremath{\Delta}S$ near the critical temperature ${T}_{c}$ can be quantitatively explained by a recently developed theory based on the London model that accounts for the strong T dependence of the model parameters near ${T}_{c}.$