Horizontal Line Nodes in Sr2RuO4 Proved by Spin Resonance

This is the authors' abstract. We don't add key points for this paper.

We investigated the low-energy incommensurate (IC) magnetic fluctuations in Sr₂RuO₄ by the high-resolution inelastic neutron scattering measurements and random phase approximation (RPA) calculations. We observed a spin resonance with energy of ωᵣes=0.56~meV centered at a characteristic wavevector Qᵣes=(0.3, 0.3, 0.5). The resonance energy corresponds well to the superconducting gap 2Δ=0.56~meV estimated by the tunneling spectroscopy. The spin resonance shows the L modulation with a maximum at around $L = 0.5$. The L modulated intensity of the spin resonance and our RPA calculations indicate that the superconducting gaps regarding the quasi-one-dimensional α and β sheets at the Fermi surfaces have the horizontal line nodes. These results may set a strong constraint on the pairing symmetry of Sr₂RuO₄. We also discuss the implications on possible superconducting order parameters.