DISORDER EFFECT ON MELTING TRANSITIONS OF VORTEX LATTICES WITH PERIODIC PINNING

Employing molecular-dynamics simulations, we study the melting transit ions in driven vortex lattices with commensurability between arrays of vortices and defects. It is shown that the lar est pinning effect can be obtained for periodic pinning arrays at zero temperature, and eith er thermal fluctuation or disorder of pinning array plays a significan t depinning role in the melting transitions of the driven vortex latti ces. As the pinning sites deviate from the periodic array, the intervo rtex interaction is found to produce an additional depinning effect on driven vortex lattices. Furthermore, enough disorder will result in a crossover from a first-order melting transition to a continuous phase transition.