Phase Transitions of Soft Disks in External Periodic Potentials: A Monte Carlo Study

摘要

The nature of freezing and melting transitions for a system of model colloidsinteracting by a DLVO potential in a spatially periodic external potential isstudied using extensive Monte Carlo simulations. Detailed finite size scalinganalyses of various thermodynamic quantities like the order parameter, itscumulants etc. are used to map the phase diagram of the system for variousvalues of the reduced screening length $kappa a_{s}$ and the amplitude of theexternal potential. We find clear indication of a reentrant liquid phase over asignificant region of the parameter space. Our simulations therefore show thatthe system of soft disks behaves in a fashion similar to charge stabilizedcolloids which are known to undergo an initial freezing, followed by are-melting transition as the amplitude of the imposed, modulating fieldproduced by crossed laser beams is steadily increased. Detailed analysis of ourdata shows several features consistent with a recent dislocation unbindingtheory of laser induced melting.