Depinning Transition of a Two Dimensional Vortex Lattice in a   Commensurate Periodic Potential
  We use Monte Carlo simulations of the 2D one component Coulomb gas on a triangular lattice, to study the depinning transition of a 2D vortex lattice in a commensurate periodic potential. A detailed finite size scaling analysis indicates this transition to be first order. No significant changes in behavior were found as vortex density was varied over a wide range. 
Violeta Gotcheva and S. Teitel