Lattice Dynamics in Quasi-Two-Dimensional Attractive Colloidal Crystals

We experimentally study lattice dynamics and phonon properties in quasi-two-dimensional (2D) colloidal crystals composed of hard-spheres with short-range attractions. The 2D colloidal crystal is formed by confining a monolayer of close-packed micron-sized polystyrene latex beads between two parallel cover glasses. The interparticle attraction is controlled via a temperature-tunable depletion interaction and the attractive potential is increased from 0 to 5 k_BT . Using video microscopy and particle tracking techniques, we obtain individual particle trajectories and investigate their dynamics as a function of interparticle attractions. By measuring the displacement correlations between particles, we extract the vibrational properties of an equivalent "shadow" system, and we show that while the lattice becomes more rigid with increasing attractions, surprisingly the microscopic spring constants become more heterogeneous across the lattice.