Re-measurement of Knight-shift on Superconducting Sr₂RuO₄

NMR experiments have been done in various unconventional superconductors, and gave information about superconducting (SC) pairing state and SC gap structure. We reported that the Knight shift at the Ru and O sites in Sr₂RuO₄ is invariant on passing through T_c.[1,2]. Quite recently, Pustogow and Luo et al. reported a reduction of the Knight shift at the O site measured with a small-energy RF pulse[3]. We reexamined ¹⁷O-NMR on our sample with similar small-energy RF pulses and reproduced their results[4]. Furthermore, we measured the temperature variation of the Knight shift by a standard spin-echo method with small-power RF pulses, and found that the spin susceptibility decreases in the SC state. We conclude that our previous results of the invariance of the Knight shift in the SC state were due to instantaneous destruction of superconductivity by theRF pulses. The heat-up effect was characterized by the temperature variation of the Knight shift under various measurement conditions. In the presentation, we will also present new results obtained near H_c2 along the ab plane.
[1] K. Ishida et al. Nature 396, 658 (1998).
[2] K. Ishida et al. Phys. Rev. B 63, 060507 (R) (2001).
[3] A. Pustogow and Y. Luo et al., Nature 574, 72 (2019).
[4] K. Ishida et al. arXiv: 1907.12236