Split superconducting and time-reversal symmetry-breaking transitions in Sr2RuO4 under stress

• Published in: Nature physics 2021-06, Vol.17 (6), p.748-754
• Main Authors: Grinenko, Vadim, Ghosh, Shreenanda, Sarkar, Rajib, Orain, Jean-Christophe, Nikitin, Artem, Elender, Matthias, Das, Debarchan, Guguchia, Zurab, Brückner, Felix, Barber, Mark E., Park, Joonbum, Kikugawa, Naoki, Sokolov, Dmitry A., Bobowski, Jake S., Miyoshi, Takuto, Maeno, Yoshiteru, Mackenzie, Andrew P., Luetkens, Hubertus, Hicks, Clifford W., Klauss, Hans-Henning
• Format: Article
• Language: English
• Subjects: 639/301; 639/766; Atomic; Broken symmetry; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Critical pressure; Electronic structure; Magnetism; Mathematical and Computational Physics; Molecular; Muon spin relaxation; Optical and Plasma Physics; Order parameters; Physics; Physics and Astronomy; Strontium; Strontium ruthenium oxide; Symmetry; Theoretical; Unconventional superconductivity
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-021-01182-7

Strontium ruthenate (Sr 2 RuO 4 ) continues to present an important test of our understanding of unconventional superconductivity, because while its normal-state electronic structure is known with precision, its superconductivity remains unexplained. There is evidence that its order parameter is chiral, but reconciling this with recent observations of the spin part of the pairing requires an order parameter that is either finely tuned or implies a new form of pairing. Therefore, a definitive resolution of whether the superconductivity of Sr 2 RuO 4 is chiral is important for the study of superconductivity. Here we report the measurement of zero-field muon spin relaxation—a probe sensitive to weak magnetism—on samples under uniaxial stresses. We observe stress-induced splitting between the onset temperatures of superconductivity and time-reversal symmetry breaking—consistent with the qualitative expectations for a chiral order parameter—and argue that this observation cannot be explained by conventional magnetism. In addition, we report the appearance of bulk magnetic order under higher uniaxial stress, above the critical pressure at which a Lifshitz transition occurs in Sr 2 RuO 4 . When strain is applied to strontium ruthenate, superconductivity emerges at a different temperature to the breaking of time-reversal symmetry. This indicates that the superconductivity could have a chiral d -wave order parameter.