Novel polarization dependence in diffusing-wave spectroscopy of crystallizing colloidal suspensions

We report an unexpected behavior of the intensity autocorrelation functions ${\mathit{C}}_{\mathit{V}\mathit{V}}$(t) (polarized) and ${\mathit{C}}_{\mathit{H}\mathit{H}}$(t) (depolarized) of multiply scattered light from dense colloidal polyball crystals under certain conditions. We find that ${\mathit{C}}_{\mathit{V}\mathit{V}}$(t) saturates at large times as expected for a frozen phase, while ${\mathit{C}}_{\mathit{H}\mathit{H}}$(t) decays to zero in a short time as in a fluid. We present a new phenomenological model for this behavior based on decoupled translational and orientational fluctuations in a weakly depolarizing medium. Our study highlights the greater sensitivity of depolarized diffusing-wave spectroscopy as a probe of the dynamics of the medium.