We present results of molecular dynamics simulations for two-dimensional repulsively interacting colloids driven by a one dimensional asymmetric and commensurate ratchet potential, switching on and off stochastically. This drives a time-averaged directed current of colloids, exhibiting resonance with change in ratcheting frequency, where the resonance frequency itself depends non-monotonically on density. Using scaling arguments, we obtain analytic results that show good agreement with numerical simulations. With increasing ratcheting frequency, we find non-equilibrium re-entrant transitions between solid and modulated liquid phases.PACS numbers: 05.40. Jc, 64.60.Cn A flashing ratchet refers to a time-averaged directed motion of Brownian particles under the influence of an spatially periodic and asymmetric potential, with the potential height varying with time, either deterministically or stochastically [1][2][3][4]. Stochastic ratcheting has been studied extensively, in the context of active dynamics of molecular motors [5][6][7][8], dynamics of colloidal dispersion in electrical [9][10][11], magnetic [12,13] or optical drive [14,15], as a mechanism of particle segregation [16][17][18], transport of cold atoms in optical lattice [19], and in the motion of flux quanta [20,21]. While a large body of work has been concentrated on the ratcheting of individual particles, fewer studies focused on the effects of interaction [22][23][24][25][26]. Recent studies of two dimensional (2D) paramagnetic particles under one dimensional (1D) magnetic ratchets observed relation between overall dynamics and local particle coordination numbers [13].In colloidal suspensions, ratchet-like directed motion of particles have been achieved using suitable laser potentials [14,15]. Confinement and laser trapping in colloids, on the other hand, is known to give rise to interesting mechanical properties and phase transitions [27][28][29][30][31][32]. Coupling 2D interacting colloids to a 1D time-independent spatially periodic potential with periodicity commensurate with the mean particle separation, leads to the phenomena of laser induced freezing (LIF) and re-entrant melting with increase in the potential strength. This was demonstrated in experiments using standing wave pattern of interfering laser beams [31,32], and was understood in terms of a dislocation unbinding theory [9,33].We consider transport of a 2D system of particles interacting via soft-core repulsion and driven by an 1D asymmetric flashing ratchet, using molecular dynamics (MD) simulations in the presence of a Langevin heat bath. The ratcheting potential breaks time-reversal symmetry and generates an average directed current along the direction of ratcheting ( Fig. 1(a)). We choose a periodicity of the potential commensurate with the inter particle separation. At switching frequencies much faster than the intrinsic relaxation times, the time scale required for particles to relax over a single valley of the external ratchet potential, the system experiences a time-averag...