Angular dependence of the latent heat of vortex-lattice melting in untwinned YBa2Cu3O7-δ

We measured the latent heat of vortex-lattice melting for varying angles Θ between the external magnetic field H and the c axis of an untwinned YBa2Cu3O7-δ single crystal. The discontinuity in entropy at melting, ΔS per unit volume of sample, depends solely on the temperature T where melting occurs, but does not depend on Θ and the corresponding melting field Hm(T,Θ). The T dependence of ΔS near the critical temperature Tc 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 Tc. copyright 1998 The American Physical Society