Pattern Switching and Polarizability for Colloids in Optical Trap Arrays

We show that colloidal molecular crystal states interacting with a periodic substrate, such as an optical trap array, and a rotating external field can undergo a rapid pattern switching in which the orientation of the crystal changes. In some cases, a martensitic-like symmetry switching occurs. It is also possible to create a polarized state where the colloids in each substrate minima develop a director field which smoothly rotates with the external drive, similar to liquid crystal behavior. These results open the possibility for creating novel types of devices using photonic band gap materials, and should be generalizable to a variety of other condensed matter systems with multiple particle trapping.