Asymmetry of the critical current and peak effect in superconducting multilayers

Abstract

The critical current Ic in Nb/NbO and Nb/Pd multilayers with different periods has been investigated in parallel magnetic fields H.TheIc(H) curves were measured for two opposite directions of the bias current Ibias (always oriented perpendicularly to the magnetic field) which causes the motion of the vortices towards the free surface of the sample and the substrate, respectively. For both directions of the current the so-called peak effect has been observed in the Ic(H) dependencies but with a large difference in the absolute values of Ic for the positive and negative directions of Ibias. The position of the peak in the Ic(H) dependencies does not depend on the direction of Ibias and it is shifted towards higher H values when the period of the multilayered structures is increased. These experimental results can be explained by considering the superposition of the applied magnetic field and the field induced by the transport current along the layers which, if the superconducting properties in different Nb layers are non-homogeneous, causes an asymmetric redistribution of the current. The effect is more pronounced when only one superconducting layer has different properties.