Evidence from tunneling spectroscopy for a quasi-one-dimensional origin of superconductivity in Sr₂RuO₄

To establish the mechanism of unconventional superconductivity in Sr₂RuO₄, 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-one-dimensional (alpha and beta) or on the quasi-two-dimensional (gamma) Fermi surfaces. We present scanning tunneling microscopy measurements of the density of states spectra in the superconducting state of Sr₂RuO₄ for 0.1T(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 approximate to 5T(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.