Vortex core deformation and stepper motor behavior in a superconducting   ratchet
  We investigated experimentally the frequency dependence of a superconducting vortex ratchet effect by means of electrical transport measurements and modeled it theoretically using the time dependent Ginzburg-Landau formalism. We demonstrate that the high frequency vortex behavior can be described as a discrete motion of a particle in a periodic potential, i.e. the so called stepper motor behavior. Strikingly, in the more conventional low frequency response a transition takes place from an Abrikosov vortex rectifier to a phase slip line rectifier. This transition is characterized by a strong increase in the rectified voltage and the appearance of a pronounced hysteretic behavior. 
J. Van de Vondel, V. N. Gladilin, A.V. Silhanek, W. Gillijns, J.   Tempere, J. T. Devreese, and V. V. Moshchalkov
cond-mat.supr-con