Vortex Dynamics Driven Transverse Transport in Superconducting Thin Films

Abstract

The generation of transverse voltage in superconducting thin films carrying a longitudinal current has been recently related to demonstrate exotic, symmetry-breaking transport phenomena. To understand the underlying phenomenon we chose two distinctly different systems to investigate; a conventional (Nb) and a nonconventional (Ni/Bi bilayer) superconductor. A systematic study of this transverse response in these type-II superconducting thin films we aimed towards establishing its microscopic origin. Both longitudinal and transverse magneto transport measurements were carried out with Hall-bar patterned devices as a function of temperature with magnetic field applied out-of-plane. In both systems, a sharp, field antisymmetric transverse resistance emerges in the superconducting transition region, closely following the field derivative of the longitudinal resistance while it was vanishingly small or absent in the fully superconducting or normal states. Based on the vortex-flow model, the behavior could be quantitatively attributed as the transverse voltage arising due to the motion of Abrikosov vortices under a combined action of Magnus like force and viscous drag force, rather than from any exotic or intrinsic Hall-type mechanism. The close correspondence between a nominally conventional superconductor Nb and an unconventional superconductor heterostructure incorporating a ferromagnetic layer indicates that the vortex dynamics alone, independent of magnetic proximity effects or unconventional pairing, seems to be sufficient to account for the observed transverse signal. Our observations while seems to provide a quantitative, material-independent model for interpreting transverse voltages in superconducting films, raises the concerns in attributing such signals to exotic physics without first ruling out conventional vortex-flow contributions.