Transport Signatures of Radial Rashba Spin-Orbit Coupling at Ferromagnet/Superconductor Interfaces

Abstract: Spin-orbit coupling (SOC) emerging at the interfaces of superconducting magnetic tunnel junctions is at the heart of multiple unprecedented physical phenomena, covering triplet proximity effects induced by unconventional (spin-flip) Andreev reflections, giant transport magnetoanisotropies, sizable tunneling anomalous Hall effects, and electrically controlled current-reversing $ 0 $--$ \pi $(-like) transitions in Josephson contacts. Recent first-principles calculations proposed that the Rashba spin-orbit fields in twisted graphene/transition-metal dichalcogenide and van der Waals multilayers can -- owing to broken mirror symmetries -- exhibit an unconventional radial component (with spin parallel to the electron's momentum), which can be quantified by the Rashba angle $ \theta_\mathrm{R} $. We theoretically explore the ramifications of radial Rashba SOC at the interfaces of vertical ferromagnet/superconductor tunnel junctions with a focus on the magnetoanisotropies of the tunneling and tunneling-anomalous-Hall-effect conductances. Our results demonstrate that $ \theta_\mathrm{R} $ can be experimentally extracted from respective magnetization-angle shifts, providing a robust way to probe the radial Rashba SOC induced by twisted multilayers that are placed as tunneling barriers between ferromagnetic and superconducting electrodes.