THERMODYNAMICS OF THE FIRST-ORDER VORTEX LATTICE MELTING TRANSITION IN YBA2CU3O7-DELTA

Using the London approximation within the high-field scaling regime, w e calculate the jump in the specific heat Delta c at the first-order m elting transition of the vortex lattice in YBa2Cu3O7-delta. This has r ecently been measured [A. Schilling et al., Phys. Rev. Lett. 78, 4833 (1997)] and reported to be at least 100 times higher than expected fro m the fluctuations of field-induced vortices alone. We demonstrate how the correct treatment of the temperature dependence of the model para meters, which are singular at the mean-field B-c2 line, leads to good agreement between the predictions of the London model and the size of the experimental jump. In addition, we consider the changes in the slo pes of the magnetization Delta(partial derivative M/partial derivative T) and Delta(partial derivative M/partial derivative H) at the transi tion. Using continuum anisotropic scaling theory we demonstrate the co nsistency of measurements at different angles of the magnetic field wi th respect to the crystal c axis.