## Flux Lattice Melting, Flux Pinning, and Superfluid Density Tensor of
YBa2Cu3O(7-delta)

#### R. Sasik and D. Stroud,
Department of Physics,
The Ohio State University, Columbus, Ohio 43210

We calculate the flux lattice melting curve T_M(H)
of YBa2Cu3O(7-delta) for a magnetic field H parallel to c,
in good agreement with experiment
without any free parameters. We expand the
Ginzburg-Landau order parameter in products of lowest Landau levels in the
ab plane and Bloch states in the c direction, evaluating the relevant
statistical averages by Monte Carlo simulation.
With no pinning, the c component of the superfluid density tensor
jumps to a finite value at the transition, but the transverse components
remain zero, corresponding to the sliding freedom of the flux lattice.
With pinning present, the in-plane components become
finite also. Relevant experiments are discussed.