Self-assembly of colloidal superstructures in coherently fluctuating fields

From microscopic fluid clusters to macroscopic droplets, the structure of fluids is governed by the van der Waals force, a force that acts between polarizable objects. In this Letter, we derive a general theory that describes the nonequilibrium counterpart to the van der Waals force, which emerges in spatially coherently fluctuating electromagnetic fields. We describe the formation of a novel and complex hierarchy of self-organized morphologies in magnetic and dielectric colloid systems. Most striking among these morphologies are dipolar foams--colloidal superstructures that swell against gravity and display a high sensitivity to the applied field. We discuss the dominance of many-body forces and derive the equation of state for a material formed by the coherent van der Waals force. Our theory is applied to recent experiments in paramagnetic colloidal systems and a new experiment is suggested to test the theory.