Vortex-lattice transition in superconducting Nb/NbZr multilayers

Abstract

Multilayers of Nb/NbZr are known to show two dimensional crossovers [three dimensional (3D) to two dimensional (2D) to 3D] in the behavior of the parallel critical field Hc2? as a function of temperature T. Here we report a systematic study of the behavior of the critical current Ic as function of the magnetic field H in the different regimes. Varied were layer thicknesses as well as the angle between H and the sample surface, and the angle between H and the current I. Apart from earlier reported nonmonotonic behavior of Ic(H), which constitutes the continuation of the 2D behavior in the H?(T) phase diagram, we find strong maxima in Ic at fields Hp far below the 2D phase line. An analysis in terms of Lorentz forces on the flux lines shows that Hp signifies a transition from a low-field region where straight vortices move freely in a direction perpendicular to the layers, to a high-field region where the vortices have developed kinks perpendicular to the layers. In this field regime Ic is determined by motion of the kinks along the layers, while the portions of the vortex parallel to the layers are pinned by an intrinsic mechanism.

Source-reported materials — not catalogue approval

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