Nonlinear transports and microvortex excitations in sheared quasi-two-dimensional dust Coulomb liquids

The microscopic spatiotemporal response of a quasi-two-dimensional dust Coulomb liquid to the shear induced by a cw laser is investigated through optical microscopy. The dust Coulomb liquid consists of many micrometer sized dust particles char,aed and suspended in a low pressure rf discharge background. Assisted by thermal fluctuations, the laser forcing enhances the cascaded generation of irregular vortices through reducing caging barriers for collective hopping. The vortex mixing leads to the mean velocity field with a simple structure that has a strong shear along the edge of the narrow laser beam. It also promotes the anomalous transverse diffusion with decaying strength from the line sourer. The viscosity and diffusion coefficient both show nonlinear dependence on the laser power under the interplay among the above nonlinear excitation and relaxation processes.