Depinning of the f=1/2 square lattice Coulomb gas model at zero temperature

The transport properties of the f = 1/2 square lattice Coulomb gas model at zero temperature are studied using Monte Carlo technique. The dependence of charge current density J on the driving electric field E is investigated by gradually increasing the electric field E from the annealed ground state. For pure system without disorder, a discontinuous depinning transition accompanying with an order-disorder transition is found when we ramp up the field. While for system with disorder, a continuous depinning transition, which obeys J similar to (E - E-c)(beta) with scaling exponent beta approximate to 1.0 for large systems, is observed. At the depinning electric field E-c, the system crossovers from a disordered pinning state to a disordered moving state. We contribute the continuous depinning transition to the depinning of system from one of a vast of metastable states to other metastable states. (c) 2005 Elsevier B.V. All rights reserved.