Spin Fluctuations in Sr${}_{1.8}$La${}_{0.2}$RuO${}_4$

Abstract

We use inelastic neutron scattering to study spin fluctuations in Sr${}_{1.8}$La${}_{0.2}$RuO${}_4$, where Lanthanum doping triggers a Lifshitz transition by pushing the van Hove singularity in the $\gamma$ band to the Fermi energy. Strong spin fluctuations emerge at an incommensurate wave vector ${\mathbf{Q}}_{ic}=(0.3,0.3)$, corresponding to the nesting vector between $\alpha$ and $\beta$ Fermi sheets. The incommensurate antiferromagnetic fluctuations shift toward $(0.25,0.25)$ with increasing energy up to $\sim 110$ meV. By contrast, scatterings near the ferromagnetic wave vectors $\mathbf{Q}=(1,0)$ and $(1,1)$ remain featureless at all energies. This contradicts the weak-coupling perspective that suggests a sharp enhancement of ferromagnetic susceptibility due to the divergence of density of states in the associated $\gamma$ band. Our findings imply that ferromagnetic fluctuations in Sr${}_2$RuO${}_4$ and related materials do not fit into the weak-coupling paradigm, but instead are quasi-local fluctuations induced by Hund's coupling. This imposes significant constraints for the pairing mechanism involving spin fluctuations.

7 pages, 4 figures

References in corpus (5)

• High Resolution Polar Kerr Effect Measurements of Sr2RuO4: Evidence for Broken Time Reversal Symmetry in the Superconducting State
• Hidden quasi one-dimensional superconductivity in Sr${}_2$RuO${}_4$
• Spin Density Wave Fluctuations and p-wave Pairing in Sr2RuO4
• Horizontal Line Nodes in Sr2RuO4 Proved by Spin Resonance
• Neutron scattering studies on spin fluctuations in Sr${}_2$RuO${}_4$