Melting of dusty plasma crystals in oscillating external fields

The melting transition of a charge-polydisperse dusty plasma crystal under the influence of a time-dependent oscillating field is studied within a sim ple model. The stochastic dynamics of the dust particles is modelled by a F okker-Planck description. Using non-equilibrium computer simulations we det ect a non-monotonic behaviour of the melting line as a function of the freq uency of the external field. This is attributed to a cage resonance effect which is controlled by the intrinsic polydispersity of the sample. The resu lts are qualitatively explained within a cage theory of the polydisperse so lid combined with a generalized Lindemann rule of melting.