We present a detailed numerical simulation study of a two dimensional system of particles interacting via the Weeks-Chandler-Anderson potential, the repulsive part of the Lennard-Jones potential. With reduction of density, the system shows a two-step melting: a continuous melting from solid to hexatic phase, followed by a a first order melting of hexatic to liquid. The solid-hexatic melting is consistent with the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario and shows dislocation unbinding. The first order melting of hexatic to fluid phase, on the other hand, is dominated by formation of string of defects at the hexatic-fluid interfaces.
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