Vortex Transport in Ni/Bi Bilayer Superconductor with Strong Spin-Orbit and Exchange Interaction

TL;DR

This study investigates vortex transport and superconductivity in Ni/Bi bilayers, revealing vortex dynamics and confirming conventional s-wave pairing despite strong spin-orbit and exchange interactions.

Contribution

It provides new insights into vortex behavior and superconductivity mechanisms in Ni/Bi bilayers with strong spin-orbit coupling and magnetic interactions.

Findings

Vortex dynamics are sensitive to out-of-plane magnetic fields.

Superconductivity extends throughout the bilayer, not just at the interface.

Transport behavior is consistent with a conventional s-wave order parameter.

Abstract

Nickel/bismuth (Ni/Bi) bilayers are a promising platform for exploring unconventional superconductivity. Ferromagnetic Ni is coupled to Bi, a strong spin orbit metal that only becomes superconducting below approx 10 mK, forming a bilayer exhibits superconductivity at a much higher temperatures, a Tc of 3 to 4 K. Such a bilayer thus makes an ideal system to probe Cooper pairing in strong spin orbit coupled magnetic environments. Magneto transport studies near Tc reveal the behavior of vortex dynamics and exchange proximity effects. It is seen that isolated vortices of the bilayers respond sensitively to out of plane fields, producing antisymmetric transverse resistance peaks attributable to competing Magnus and viscous forces. Control experiments using a ferromagnetic insulator confirm that superconductivity extends throughout the bilayer, not just confined at the interface. Overall, the results provide a unified picture of transport dominated by vortex dynamics and show that a conventional s wave order parameter accounts for the observations, with any likely unconventional contributions being only subtle.