We simulate a rotating 2D BEC to study the melting of a vortex lattice in
presence of random impurities. Impurities are introduced either through a
protocol in which vortex lattice is produced in an impurity potential or first
creating the vortex lattice in the absence of random pinning and then cranking
up the (co-rotating) impurity potential. We find that for a fixed strength,
pinning of vortices at randomly distributed impurities leads to the new states
of vortex lattice. It is unearthed that the vortex lattice follow a two-step
melting via loss of positional and orientational order. Also, the comparisons
between the states obtained in two protocols show that the vortex lattice
states are metastable states when impurities are introduced after the formation
of an ordered vortex lattice. We also show the existence of metastable states
which depend on the history of how the vortex lattice is created.Comment: Accepted in Euro. Phys. Let
