Effect of Fluctuations on the Freezing of a Colloidal Suspension in an External Periodic Potential

We incorporate the effects of fluctuations in a density functional analysis of the freezing of a colloidal liquid in the presence of an external potential generated by interfering laser beams. A mean field treatment, using a density functional theory, predicts that with the increase in the strength of the modulating potential, the freezing transition changes from a first order to a continuous one via a tricritical point for a suitable choice of the modulating wavevectors. We demonstrate here that the continuous nature of the freezing transition at large values of the external potential $V_{e}$ survives the presence of fluctuations. We also show that fluctuations tend to stabilize the liquid phase in the large $V_{e}$ regime.