2004/05/12 by R. Agra, F. van Wijland, E. Trizac · 1 citation
Physics and Astronomy · #cond-mat.stat-mech #cond-mat.soft
paper · pdf · doi:10.1103/physrevlett.93.018304
published as Phys. Rev. Lett. 93, 018304 (2004). · 4 pages, to appear in Phys. Rev. Lett
arxiv created 2004/05/12 · arxiv updated 2009/12/01
Freezing of charged colloids on square or triangular two-dimensional periodic substrates has been recently shown to realize a rich variety of orientational orders. We propose a theoretical framework to analyze the corresponding structures. A fundamental ingredient is that a non spherical charged object in an electrolyte creates a screened electrostatic potential that is anisotropic at any distance. Our approach is in excellent agreement with the known experimental and numerical results, and explains in simple terms the reentrant orientational melting observed in these so called colloidal molecular crystals. We also investigate the case of a rectangular periodic substrate and predict an unusual phase transition between orientationnaly ordered states, as the aspect ratio of the unit cell is changed.