Spin Susceptibility of the Topological Superconductor UPt3 from Polarized Neutron Diffraction

Experiment and theory indicate that ${\mathrm{UPt}}_{3}$ is a topological superconductor in an odd-parity state, based in part from the temperature independence of the NMR Knight shift. However, quasiparticle spin-flip scattering near a surface, where the Knight shift is measured, might be responsible. We use polarized neutron scattering to measure the bulk susceptibility with $H\ensuremath{\parallel}c$, finding consistency with the Knight shift but inconsistency with theory for this field orientation. We infer that neither spin susceptibility nor a Knight shift are a reliable indication of odd parity.