Symmetry-breaking density profiles in confined liquids

Density profiles of a liquid confined between two parallel plates are studied near a liquid-gas transition. The system is additionally exposed to an external field depending on the coordinate perpendicular to the plates that possesses a discrete left-right symmetry with respect to the midplane between the plates. It is found that the equilibrium density profiles can be symmetry breaking, i.e., they do not possess the discrete left-right symmetry of the external field. Explicit results are obtained within a simple double-slit model consisting of two layers of two-dimensional Lennard-Jones systems using both computer simulation and density-functional theory. Such symmetry-breaking profiles should be observable in confined colloidal suspensions.