Disorder-induced superconducting ratchet effect in nanowires

A dc voltage drop develops along amorphous indium oxide wires that are exposed to an ac bias source. This voltage is antisymmetric with the magnetic field and is characterized by sample specific quasiperiodic magnetovoltage oscillations. The voltage magnitude increases with decreasing temperature below T_C but saturates at low T. As the disorder of the sample is decreased, the dc voltage is suppressed. This rectification is attributed to a superconducting ratchet effect in which disorder and geometrical confinement play the role of asymmetric pinning centers. This effect demonstrates the importance of inherent inhomogeneity and vortex motion in both sides of the superconductor-insulator transition of disordered superconductors.