Reduction of the spin susceptibility in the superconducting state of Sr2RuO4 observed by polarized neutron scattering

Abstract

Recent observations [A.~Pustogow et al. Nature 574, 72 (2019)] of a drop of the ${}^{17}$O nuclear magnetic resonance (NMR) Knight shift in the superconducting state of Sr${}_2$RuO${}_4$ challenged the popular picture of a chiral odd-parity paired state in this compound. Here we use polarized neutron scattering to show that there is a $34\pm 6$ % drop in the magnetic susceptibility at the ruthenium site below the superconducting transition temperature. Measurements are made at lower fields $H\sim \frac{1}{3}{H}_{c2}$ than a previous study allowing the suppression to be observed. Our results are consistent with the recent NMR observations and rule out the chiral odd-parity $\mathbf{d}=\hat{\mathbf{z}}(k_x\pm i{k}_y)$ state. The observed susceptibility is consistent with several recent proposals including even-parity $B_{1g}$ and odd-parity helical states.

New version with Supplementary Material discussing orbital contributions to the susceptibility, Fermi liquid corrections and a two fluid model