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

TL;DR

This study uses superconducting tunneling spectroscopy to investigate intrinsic spin-orbit coupling and orbital depairing in Nb-doped SrTiO$_3$, revealing short spin-orbit scattering times and the significant role of heavy electron bands in pairing.

Contribution

It provides a quantitative evaluation of spin-orbit scattering times and highlights the importance of heavy electron bands in superconductivity in SrTiO$_3$.

Findings

Spin-orbit scattering time $ au_{so} \,\leq 1.1$ ps.

Orbital depairing is suppressed in the 2D limit.

Heavy electron band significantly contributes to pairing.

Abstract

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 $\tau_{so} \leq 1.1$ 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$_3$.