We reexamine the density functional theory of laser-induced freezing, i.e., the freezing of a colloidal liquid into crystalline order in the presence of an external periodic modulating potential $V_e$ with its wave vectors tuned to the ordering wave vector in the liquid phase. We show definitively that the initial first order freezing transition (at small $V_e$) changes to a continuous one (at large $V_e$) via a tricritical point provided the modulation wave vectors are suitably chosen. We also present predictions for the parameter values of the tricritical points for a realistic colloidal system.

• Received 15 October 1993

DOI:https://doi.org/10.1103/PhysRevLett.73.2923