  Dielectric particles in weakly conducting fluids rotate spontaneously when
subject to strong electric fields. Such Quincke rotation near a plane electrode
leads to particle translation that enables physical models of active matter.
Here, we show that Quincke rollers can also exhibit oscillatory dynamics,
whereby particles move back and forth about a fixed location. We explain how
oscillations arise for micron-scale particles commensurate with the thickness
of a field-induced boundary layer in the nonpolar electrolyte. This work
enables the design of colloidal oscillators.
