Abstract
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.
Highlights
The Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity is one of the cornerstones of condensed-matter physics [1]
The superconducting density of states of the two-dimensional electron system at the LaAlO3–SrTiO3 interface exhibits broad quasiparticle peaks that are well described by the Dynes parameter
The strong temperature dependence at low temperatures rules out inelastic electron scattering and magnetic scattering as the origin of the pair breaking
Summary
The Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity is one of the cornerstones of condensed-matter physics [1]. The theory correctly predicts that superconductors are characterized by the appearance of a gap in the electron density of states below the critical temperature Tc. The magnitude of the gap scales with Tc and the spectral weight accumulates in sharp quasiparticle peaks bordering the gap. The magnitude of the gap scales with Tc and the spectral weight accumulates in sharp quasiparticle peaks bordering the gap These quasiparticle peaks in the density of states are broader than the expectation of the BCS theory in several superconductors. Dynes et al attributed this broadening to the finite lifetime of the quasiparticle states by inserting a phenomenological parameter in the equation for the density of states N: N (E ) = Re E −i (1).
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