from oxygen-17 nuclear magnetic resonance*

The superconducting state of the quasi two-dimensional and strongly correlated perovskite Sr₂RuO₄ is considered to be a solid-state analogue to the superfluid ³He-A phase, with an odd-parity order parameter that breaks time-reversal symmetry. Recent experiments using in-plane uniaxial stress revealed a dramatic rise and peak of the transition temperature [1], related to a DOS enhancement [2]. Here we use ¹⁷O NMR spectroscopy to probe the nature of superconductivity in Sr₂RuO₄ and its evolution under uniaxial strain. A reduction of the Knight shift is observed below T_c for all strain values, consistent with a drop in spin polarization in the superconducting state [3]. In unstrained samples, our results rule out a chiral p-wave order parameter. We discuss the issue of sample heating on a sub-millisecond time scale after the NMR pulse, which is particularly relevant to superconductors with a small transition temperature (T_c ≈ 1 K).

[1] Science 355, eaaf9398 (2017)
[2] Phys. Rev. X, 9, 021044 (2019)
[3] Nature 574, 72–75 (2019)