Colloids in a periodic potential: driven lattice gas in continuous space

TL;DR

This study models colloidal particles in a periodic potential, revealing equilibrium condensation and driven phase behaviors, with implications for optical tweezer experiments and lattice gas analogs.

Contribution

It introduces a continuous-space colloidal model that exhibits lattice gas-like condensation and driven phase transitions, bridging experimental colloid systems and theoretical lattice models.

Findings

Equilibrium system shows condensation similar to lattice gas.

Weak drive induces ordering into high- and low-density regions.

Strong bias disrupts order and causes large energy fluctuations.

Abstract

Motivated by recent studies of colloidal particles in optical tweezer arrays, we study a two-dimensional model of a colloidal suspension in a periodic potential. The particles tend to stay near potential minima, approximating a lattice gas. The interparticle interaction, a sum of Yukawa terms, features short-range repulsion and attraction at somewhat larger separations, such that two particles cannot occupy the same potential well, but occupation of adjacent cells is energetically favored. Monte Carlo simulation reveals that the equilibrium system exhibits condensation, as in the Ising model/lattice gas with conserved magnetization; the transition appears to be continuous at a half occupancy. We study the effect of biased hopping probabilities favoring motion along one lattice direction, as might be generated by a steady flow relative to the potential array. This system is found to exhibit features of the driven lattice gas: the interface is oriented along the drive, and appears to be smooth. A weak drive facilitates ordering of the particles into high- and low-density regions, while stronger bias tends to destroy order, and leads to very large energy fluctuations. Our results suggest possible realizations of equilibrium and driven lattice gases in a colloidal suspension subject to an optical tweezer array.