Physical Review Letters ( IF 8.385 ) Pub Date :
A. N. Petsch; M. Zhu; Mechthild Enderle; Z. Q. Mao; Y. Maeno; I. I. Mazin; S. M. Hayden

Recent observations [A.~Pustogow .~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 (PNS) to show that there is a $34±6$,% drop in the magnetic susceptibility at the Ru site below the superconducting transition temperature. We measure at lower fields $H\sim \frac{1}{3}{H}_{c2}$ than a previous PNS study allowing the suppression to be observed. The PNS measurements show a smaller susceptibility suppression than NMR measurements performed at similar field and temperature. Our results rule out the chiral odd-parity $𝐝=\stackrel{̂}{𝐳}\left({k}_{x}±i{k}_{y}\right)$ state and are consistent with several recent proposals for the order parameter including even-parity ${B}_{1g}$ and odd-parity helical states.

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