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, "l ens," or fluxon "rectifier" because the applied electrical ac is transforme d into a net de motion of fluxons. Thermal fluctuations and the asymmetry o f the ratchet channel walls induce this "diode" effect, which can have impo rtant applications in devices, such as SQUID magnetometers, and for fluxon optics, includings convex and concave fluxon lenses. Certain features are u nique to this novel two-dimensional (2D) geometric pump, and different from the previously studied 1D ratchets.