Intrinsic spin-orbit coupling in superconducting delta-doped SrTiO3 heterostructures

We report the violation of the Pauli limit due to intrinsic spin-orbit coupling in SrTiO3 heterostructures. Via selective doping down to a few nanometers, a two-dimensional superconductor is formed, geometrically suppressing orbital pair breaking. The spin-orbit scattering is exposed by the robust in-plane superconducting upper critical field, exceeding the Pauli limit by a factor of 4. Moreover, transport scattering times several orders of magnitude higher than for conventional thin-film superconductors enable this system to enter a different regime of cleanliness, where intrinsic band spin-orbit coupling effects arise in these symmetrically doped samples.