Determination of spin-orbit scattering lifetime at the interface of LaAlO_{3}/SrTiO_{3} from the superconducting upper critical fields

Abstract

The intrinsic mechanism of the spin-orbit coupling at the LaAlO_{3}/SrTiO_{3} 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 spin-orbit coupling was also shown to play an important role, particularly when the Fermi level is close to the Lifshitz point. In this paper, we focus on the measurements of the anisotropic superconducting upper critical fields in gated LaAlO_{3}/SrTiO_{3} devices. By rigorous fittings of the H_{c2}-T curves using both the Werthamer-Helfand-Hohenberg theory and Klemm-Luther-Beasley model, an upper limit of the spin-orbit scattering lifetime can be determined in the two-dimensional limit of the superconducting state. We found that the extracted spin-orbit scattering lifetime monotonically increases with the effective transport lifetime that spans over two orders of magnitude in the regime with sheet density close to and higher than that at the Lifshitz point. Those results suggest the dominant role of Elliott-Yafet type spin relaxation. The comparison to the weak localization fittings on magnetoconductance reveals a striking difference. Such a model dependence infers an electronic phase separation at the LaAlO_{3}/SrTiO_{3} interface, where the superconductivity originates from a selective d-subband occupancy.