Determination of Spin-Orbit Scattering Lifetime at the Interface of LaAlO₃/SrTiO₃ from the Superconducting Upper Critical Fields

The intrinsic mechanism of the spin-orbit coupling at the LaAlO₃ / SrTiO₃ interface remains a debatable issue. Rashba-type spin-orbit coupling is an appealing candidate that has been demonstrated by several magnetotransport results. On the other hand, the atomic spinorbit coupling was also shown to play an important role, particularly when the Fermi level is close to the Liftshitz point. Unlike previous works, we focus on the measurements of the anisotropic and superconducting upper critical fields in gated LaAlO₃ / SrTiO₃ devices. By rigorous fittings of the H_c2-T curves using both the Werthamer-Helfand-Hohenberg theory
and Klemm-Luther-Beasley model, the spin-orbit scattering lifetime can be determined with high precision in superconducting state. We found that the extracted spin-orbit lifetime monotonically increase with the transport lifetime that spanned over two orders of magnitude in the regime with sheet density higher than that at Liftshitz point. Those results suggest the dominant role of Elliott-Yafet type spin-relaxation. Comparison to the weak localization fittings will be presented and discussed.