  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.
