Superconducting fluxon pumps and lenses

We study stochastic transport of fluxons in superconductors by alternating current (ac) rectification. Our simulated system provides a fluxon pump, ``lens,'' or fluxon ``rectifier'' because the applied electrical ac is transformed into a net dc motion of fluxons. Thermal fluctuations and the asymmetry of the ratchet channel walls induce this ``diode'' effect, which can have important applications in devices, such as SQUID magnetometers, and for fluxon optics, including convex and concave fluxon lenses. Certain features are unique to this novel two-dimensional (2D) geometric pump, and different from the previously studied 1D ratchets.