Vortex lattice melting in layered superconductors with periodic columnar pins.

The melting of the vortex lattice in highly anisotropic, layered superconductors with commensurate, periodic columnar pins is studied in a geometry where magnetic field and columnar pins are normal to the layers. Thermodynamic properties and equilibrium density distributions are obtained from numerical minimization of an appropriate free-energy functional. We find a line of first-order transitions that ends at a critical point as the pin concentration is increased. We quantitatively determine the location of this critical point and show that it is experimentally accessible.