SHEAR-INDUCED MELTING OF 2-DIMENSIONAL SOLIDS

We have carried out detailed nonequilibrium molecular-dynamics simulation studies of the shear-induced melting transition of a model two-dimensional solid. We find that the shear melting of the two-dimensional soft-disk solid at temperature T=1 and density rho=1.03 occurs in two stages: (1) a transition from elastic to plastic behavior takes place as soon as any finite shear rate is applied; (2) qualitative changes in structural and dynamic behavior occur near a shear rate of gamma=0.07. For gamma less than or similar to 0.07, the system possesses very long-range bond-orientational correlations, and the instantaneous static structure factor exhibits pronounced sixfold anisotropy, with a sixfold pattern that rotates uniformly with time in response to the applied shear. For gamma greater than or similar to 0.07, the system behaves like an ordinary two-dimensional liquid under shear in that the ranges of translational and bond-orientational correlations are comparable and the instantaneous static structure factor does not exhibit persistent sixfold anisotropy. We discuss our results in terms of the two competing possibilities of a Kosterlitz-Thouless-Halperin-Nelson-Young two-stage melting scenario or a single first-order melting transition.