Neutron scattering studies on spin fluctuations in Sr$_2$RuO$_4$

TL;DR

This study investigates magnetic excitations in Sr$_2$RuO$_4$ using neutron scattering, revealing persistent nesting signals and quasi-ferromagnetic contributions across a wide temperature range without resonance in the superconducting phase.

Contribution

It provides detailed neutron scattering data on spin fluctuations in Sr$_2$RuO$_4$, highlighting the temperature dependence and nature of magnetic excitations.

Findings

Nesting signals weaken at low energies with increasing temperature.

No resonance excitation observed in the superconducting phase.

Quasi-ferromagnetic contributions remain robust across temperatures.

Abstract

The magnetic excitations in Sr$_2$RuO$_4$ are studied by polarized and unpolarized neutron scattering experiments as a function of temperature. At the scattering vector of the Fermi-surface nesting with a half-integer out-of-plane component, there is no evidence for the appearance of a resonance excitation in the superconducting phase. The body of existing data indicates weakening of the scattered intensity in the nesting spectrum to occur at very low energies. The nesting signal persists up to 290 K but is strongly reduced. In contrast, a quasi-ferromagnetic contribution maintains its strength and still exhibits a finite width in momentum space.