Sr₂RuO₄ has stood as the leading candidate for a spin-triplet superconductor for 26 years¹. However, recent NMR experiments have cast doubt on this candidacy^2,3 and it is difficult to find a theory of superconductivity that is consistent with all experiments. The order parameter symmetry for this material therefore remains an open question. Symmetry-based experiments are needed that can rule out broad classes of possible superconducting order parameters. Here, we use resonant ultrasound spectroscopy to measure the entire symmetry-resolved elastic tensor of Sr₂RuO₄ through the superconducting transition. We observe a thermodynamic discontinuity in the shear elastic modulus c₆₆, which implies that the superconducting order parameter has two components. A two-component p-wave order parameter, such as p_x + ip_y, naturally satisfies this requirement. As this order parameter appears to have been precluded by recent NMR experiments, we suggest that two other two-component order parameters, namely \(\{{d}_{xz},{d}_{yz}\}\) and \(\{{d}_{{x}^{2}-{y}^{2}},{g}_{xy({x}^{2}-{y}^{2})}\}\), are now the prime candidates for the order parameter of Sr₂RuO₄.

Sr ₂ RuO ₄成为自旋三重超导体的领先候选人已有26年¹。但是，最近的NMR实验对该候选资格^2,3提出了质疑，并且很难找到与所有实验都一致的超导理论。因此，这种材料的顺序参数对称性仍然是一个悬而未决的问题。需要基于对称的实验，以排除可能的超导阶参数的大类。在这里，我们使用共振超声光谱通过超导转变来测量Sr ₂ RuO ₄的整个对称分辨的弹性张量。我们观察到剪切弹性模量的热力学不连续性c ₆₆，这意味着超导阶数参数具有两个分量。两分量的p波阶参数（例如p _x  +  i p _y）自然可以满足此要求。由于该阶跃参数似乎已被最近的NMR实验所排除，因此我们建议使用另外两个两个分量的阶跃参数，即\（\ {{d} _ {xz}，{d} _ {yz} \} \）和\（\ {{d} _ {{x} ^ {2}-{y} ^ {2}}，{g} _ {xy（{x} ^ {2}-{y} ^ {2}）} \} \），现在是Sr ₂ RuO ₄的有序参数的主要候选者。