Experimental observation of two-stage melting in a classical two dimensional screened Coulomb system.

We have observed a two-stage melting transition in a two-dimensional (2D) ultra-clean colloidal suspension of highly charged, submicron sized spheres in water using optical microscopy and digital imaging. Our system is confined between two flat glass plates, has a lateral extent of at least 1000 spheres, and has equilibrated for over 10(5) time steps. Direct observation of topological defects and computed correlation functions from real space images give insight into nature of the 2D melting process.