Spin fluctuations in Sr$_2$ RuO$_4$ from polarized neutron scattering: implications for superconductivity
Résumé
Triplet pairing in Sr$_2$RuO$_4$ was initially suggested based on the hypothesis of strong ferromagnetic spin fluctuations. Using polarized inelastic neutron scattering, we accurately determine the
full spectrum of spin fluctuations in Sr$_2$RuO$_4$. Besides the well-studied incommensurate magnetic
fluctuations we do find a sizeable quasiferromagnetic signal, quantitatively consistent with all macroscopic and microscopic probes. We use this result to address the possibility of magnetically-driven
triplet superconductivity in Sr$_2$RuO$_4$. We conclude that, even though the quasiferromagnetic signal is stronger and sharper than previously anticipated, spin fluctuations alone are not enough to
generate a triplet state strengthening the need for additional interactions or an alternative pairing
scenario.
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