Superconducting tunneling spectroscopy of spin-orbit coupling and orbital depairing in Nb:SrTiO${}_3$

We have examined the intrinsic spin-orbit coupling (SOC) and orbital depairing in thin films of Nb-doped SrTiO${}_3$ by superconducting tunneling spectroscopy. The orbital depairing is geometrically suppressed in the two-dimensional limit, enabling a quantitative evaluation of the Fermi level spin-orbit scattering using Maki’s theory. The response of the superconducting gap under in-plane magnetic fields demonstrates short spin-orbit scattering times ${\tau }_{so}\le 1.1$ ps. Analysis of the orbital depairing indicates that the heavy electron band contributes significantly to pairing. These results suggest that the intrinsic spin-orbit scattering time in SrTiO${}_3$ is comparable to those associated with Rashba effects in SrTiO${}_3$ interfacial conducting layers and can be considered significant in all forms of superconductivity in SrTiO${}_3$.