Some possible effects of periodic pinning in high T-c superconductors

We are assuming that the pinning points could be created in the center of each unit cell of the planar superconducting lattice. The existence of periodic pinning suggests a particular dynamics of vortices in the mixed state of 2D and 3D high T-c superconductors. Such a moving mechanism may be studied using a planar Ports model. We used such a model to perform some numerical simulations focusing on the melting of the Abrikosov lattice of vortices in a system of Josephson arrays of superconducting grains. A Monte Carlo analysis on the resulting hamiltonian in a field given by a starting filling factor of f = 1/2 exhibits two phase transitions, in both 2D and 3D. The 2D model gives the critical temperatures T-cl similar or equal to 0.325 and T-m similar or equal to 0.65. The 3D one gives T-cl similar or equal to 0.67 and T-m similar or equal to 1.325. The numerical estimation of the Challa parameters for both transitions indicates their continuous nature in both 2D and 3D versions of this model. The results suggest that, below TT,I, the superconductor is in the Meissner phase, between T-cl and T-m it is in the mixed state and above T-m it is in the melted flux state, i.e. technological normal slate. (C) 1997 Academic Press Limited.