  Weak anti-localization offers an experimental tool to address spin--orbit
coupling of two-dimensional oxide surfaces and interfaces via
magneto-transport. To overcome the shortcomings of the formulation for
single-band spin-1/2 electrons, we consider an effective three-band model that
allows a decomposition into a pseudo-spin representation 1/2+3/2. Whereas the
well-established spin-1/2 transport signature results from the singlet and
triplet sectors in the Cooperon equation, a new structure originates from the
quintet and septet sectors generated by the spin 3/2x3/2 representation.
