Evidence from Tunneling Spectroscopy for a Quasi-One Dimensional Origin of Superconductivity in Sr2RuO4

TL;DR

This study uses tunneling spectroscopy to investigate the momentum-space structure of energy gaps in Sr2RuO4, providing evidence that superconductivity primarily originates from quasi-one-dimensional Fermi surfaces with line nodes.

Contribution

It offers direct spectroscopic evidence supporting the quasi-one-dimensional origin of superconductivity in Sr2RuO4, highlighting the role of the $eta$ and $eta$ bands in pairing.

Findings

Single superconducting gap with 2Δ ≈ 5 T_C observed.

Spectral shape suggests line nodes in the energy gap.

Results consistent with magnetically mediated odd-parity pairing.

Abstract

To establish the mechanism of unconventional superconductivity in Sr$_2$RUO$_4$, a prerequisite is direct information concerning the momentum-space structure of the energy gaps $\Delta_i(k)$, and in particular whether the pairing strength is stronger ("dominant") on the quasi-1D ($\alpha$ and $\beta$) or on the quasi-2D ($\gamma$) Fermi surfaces. We present scanning tunneling microscopy (STM) measurements of the density-of-states spectra in the superconducting state of Sr$_2$RuO$_4$ for $0.1 T_C<T<T_C$, and analyze them, along with published thermodynamic data, using a simple phenomenological model. We show that our observation of a single superconducting gap scale with maximum value $2\Delta \approx 5 T_C$ along with a spectral shape indicative of line nodes is consistent, within a weak-coupling model, with magnetically mediated odd-parity superconductivity generated by dominant, near-nodal Cooper pairing on the $\alpha$ and $\beta$ bands.