Microscopic origin of the Dynes parameter Γ of the LaAlO 3 – SrTiO 3 interface superconductor

The superconducting density of states of the two-dimensional electron system at the ${\mathrm{LaAlO}}_{3}--{\mathrm{SrTiO}}_{3}$ interface exhibits broad quasiparticle peaks that are well described by the Dynes parameter $\mathrm{\ensuremath{\Gamma}}$. We measured $\mathrm{\ensuremath{\Gamma}}$ in a wide range of temperatures and gate voltages using tunneling spectroscopy. $\mathrm{\ensuremath{\Gamma}}$ exhibits a ${T}^{q}$ temperature dependence, with $q=2.2\ifmmode\pm\else\textpm\fi{}0.2$. We discuss several interpretations of $\mathrm{\ensuremath{\Gamma}}$ and conclude that $\mathrm{\ensuremath{\Gamma}}$ is an intrinsic parameter of the superconducting state that quantifies the effect of the pair-breaking processes in the superconductor. The strong temperature dependence at low temperatures rules out inelastic electron scattering and magnetic scattering as the origin of the pair breaking. We find that $\mathrm{\ensuremath{\Gamma}}$ can be explained by interband scattering and by scattering in a superconductor with nodes in the order parameter.