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#### Thermodynamic evidence for a two-component superconducting order parameter in Sr_{2}RuO_{4}

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Ghosh, S., Shekhter, A., Jerzembeck, F., Kikugawa, N., Sokolov, D. A., Brando, M., et al. (2021).
Thermodynamic evidence for a two-component superconducting order parameter in Sr_{2}RuO_{4}.*
Nature Physics,* *17*, 199-204. doi:10.1038/s41567-020-1032-4.

Cite as: http://hdl.handle.net/21.11116/0000-0007-0F0D-C

##### Abstract

Sr2RuO4 has stood as the leading candidate for a spin-triplet superconductor for 26 years1. However, recent NMR experiments have cast doubt on this candidacy2,3 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 px + ipy, 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 $$\{{d}_{xz},{d}_{yz}\}$${dxz,dyz} and $$\{{d}_{{x}^{2}-{y}^{2}},{g}_{xy({x}^{2}-{y}^{2})}\}$${dx2−y2,gxy(x2−y2)}, are now the prime candidates for the order parameter of Sr2RuO4.