Crossover from Intermittent to Continuum Dynamics for Locally Driven Colloids

We simulate a colloid with charge $q_d$ driven through a disordered assembly of interacting colloids with charge $q$ and show that, for $q_d \approx q$, the velocity-force relation is nonlinear and the velocity fluctuations of the driven particle are highly intermittent with a $1/f$ characteristic. When $q_d \gg q$, the average velocity drops, the velocity force relation becomes linear, and the velocity fluctuations are Gaussian. We discuss the results in terms of a crossover from strongly intermittent heterogeneous dynamics to continuum dynamics. We also make several predictions for the transient response in the different regimes.