Nonequilibrium stationary states with ratchet effect.

An ensemble of particles in thermal equilibrium at temperature T, modeled by Nosè-Hoover dynamics, moves on a triangular lattice of oriented semidisk elastic scatterers. Despite the scatterer asymmetry, a directed transport is clearly ruled out by the second law of thermodynamics. Introduction of a polarized zero mean monochromatic field creates a directed stationary flow with nontrivial dependence on temperature and field parameters. We give a theoretical estimate of directed current induced by a microwave field in an antidot superlattice in semiconductor heterostructures.