Signatures of Rashba and Rashba-Edelstein effect in charge and spin transport properties of elemental Bismuth thin films

The (111) surface of elemental bismuth has been associated with a large Rashba spin-orbit coupling that can lead to significant spin polarization of carriers, and also conversion of charge currents to spin-accumulation via the Rashba-Edelstein (RE) effect. However, direct evidence for the RE effect in transport properties has been lacking. Using magnetotransport measurements, we present evidence for high-mobility, two-dimensional surface states in epitaxially grown Bi (111) thin films, that begin to dominate charge transport below a characteristic temperature Ts ~ 100 K. We also conduct spin-torque ferromagnetic resonance (ST-FMR) measurements on Bi (111)/Permalloy bilayers. We observe a significant increase in the damping like torque below Ts, consistent with enhanced spin transport across the Bi/Permalloy interface. We relate our observations to the spin-momentum locking at Bi (111) surfaces.