Melting dynamics in thermal and stress driven Coulomb clusters

The microscopic dynamical responses of a two dimensional circular Coulomb cluster to thermal excitations and to the external force along a narrow band through its center are studied. The strong competition between the circular boundary and the inner domain with triagular lattice leads to the nonuniform melting of the cluster. With the increasing temperature, the surface particles exhibit anisotropic motions along the circular shells. No abrupt melting transition is observed for the outer region. The intrinsic defects around the domain boundary initiate the continuous core melting transition and also the fluidization under the external stress. The fluidization shows a non-equilibrium second order transition with stick-slip type motion at the transition point.