Reduced spin suscpetibility in superconducting Sr₂RuO₄ measured by polarized neutron diffraction

Superconducting Sr₂RuO₄ has previously been considered as an analogue of superfluid ³He-A [1]. But the picture of odd-order parameter superconductivity with chiral triplet-pairing got recently challenged by the observation of a drop in the ¹⁷O-NMR Knight shift below the superconducting transition [2]. Herein, we present new data on the magnetic susceptibility in Sr₂RuO₄ collected by polarized neutron scattering. Consistent with the observations in NMR, a reduction below the superconducting transition is observed. In relation to previous work [3] we propose a complicated field dependence alongside large residual susceptibilities at zero temperature, arising from orbital and spin-orbit contributions. Our results support singlet-pairing with a complicated gap-symmetry or triplet-pairing with an in-plane d-vector, where time-reversal symmetry is still broken [4].

[1] Maeno et al., Nature 372, 532 (1994); Rice et al., J. Phys.: Condens. Matter 7, L643 (1995)
[2] Pustogow et al., arXiv:1904.00047 (2019)
[3] Duffy et al., Phys. Rev. Lett. 85, 5412 (2000)
[4] Luke et al., Nature 394, 558 (1998); Xia et al., Phys. Rev. Lett. 97, 167002 (2006)