Nonlinear ac response of an unpinned two-dimensional Wigner crystal - art.no. 073401

We analyze the macroscopic response of an unpinned two-dimensional Wigner c rystal (WC) for the case of nonlinear losses with a nonuniform ac excitatio n in the Corbino geometry. For a WC above a liquid-helium surface, the nonl inearity arises from the Bragg-Cherenkov resonance, which gives saturation of the drift velocity with driving force. We present an analytical theory o f the current distribution in the vicinity of the resonance. The theory rel ates the measured magnetoconductivity of WC to the microscopic characterist ics of the resonance, in particular to the low-velocity tail of the frictio nal force.