  Using both dynamical density functional theory and particle-resolved Brownian
dynamics simulations, we explore the flow of two-dimensional colloidal solids
and fluids driven through a linear channel with a geometric constriction. The
flow is generated by a constant external force acting on all colloids. The
initial configuration is equilibrated in the absence of flow and then the
external force is switched on instantaneously. Upon starting the flow, we
observe four different scenarios: a complete blockade, a monotonic decay to a
constant particle flux (typical for a fluid), a damped oscillatory behaviour in
the particle flux, and a long-lived stop-and-go behaviour in the flow (typical
for a solid). The dynamical density functional theory describes all four
situations but predicts infinitely long undamped oscillations in the flow which
are always damped in the simulations. We attribute the mechanisms of the
underlying stop-and-go flow to symmetry conditions on the flowing solid. Our
predictions are verifiable in real-space experiments on magnetic colloidal
monolayers which are driven through structured microchannels and can be
exploited to steer the flow throughput in microfluidics.
