¹⁷ O Knight shift study in the superconducting state of Sr₂RuO₄

¹⁷ O Knight shift measurements in Sr₂RuO₄ were performed over the wide range of magnetic field 3.2-11.4kOe parallel to the basal RuO₂ planes. The spin susceptibility is totally unchanged through its T_c, evidencing that the spin-triplet superconducting state is realized in Sr₂RuO₄. The result indicates that the Cooper pairs consist of the parallel spin pairs | ↑↑> and | ↑↑> with their quantization axis perpendicular to the c-axis direction. The in-plane 2D nearly ferromagnetic spin fluctuations may play a role for the stabilization of this state among various representations of spin-triplet order parameter.