Depinning phase transitions in two-dimensional lattice Coulomb solids

Collective depinning transitions in Coulomb solid-on-a-lattice systems are investigated in the low-charge-density limit. It is argued that depinning occurs at an inverted, continuous, dislocation unbinding transition of the Halperin-Nelson type. The depinning transition temperature is shown to be linear in the charge density, with a slope which is in good agreement with recent Monte Carlo simulations.