Evidence for surface states and superconducting critical field modulation at the Ni-Bi interface

We report weak anti-localization measurements suggestive of high-mobility, two-dimensional surface states in epitaxially grown Bi (111) thin films, which have been shown to have a large Rashba spin-orbit coupling effect. Weak anti-localization (WAL) cusps in the magnetoresistance are sharper for out-of-plane fields vs in-plane fields, suggestive of dimensional confinement. The WAL cusps show uniformity in behavior for field orientations in the plane of sample, regardless of the relative direction of current flow. Additionally, by growing a nickel layer on the Bi (111) surface, we observe superconductivity with modulation of the critical field as the applied field is rotated in the sample plane. Angular frequency, sign, and magnitude of this effect are explored with respect to Bi layer thickness, temperature, lattice orientation, and current direction, which provide evidence for tuning of superconducting properties due to the angular anisotropy of the spin-split surface states.