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Time-reversal symmetry-breaking superconductivity in Sr2RuO4

Nature volume 394, pages 558–561 (1998)Cite this article

Abstract

Although the properties of most superconducting materials are well described by the theory1 of Bardeen, Cooper and Schrieffer (BCS), considerable effort has been devoted to the search for exotic superconducting systems in which BCS theory does not apply. The transition to the superconducting state in conventional BCS superconductors involves the breaking of gauge symmetry only, whereby the wavefunction describing the Cooper pairs—the paired electron states responsible for superconductivity—adopt a definite phase. In contrast, a signature of an unconventional superconducting state is the breaking of additional symmetries2, which can lead to anisotropic pairing (such as the ‘d-wave’ symmetry observed in the copper oxide superconductors) and the presence of multiple superconducting phases (as seen in UPt3 and analogous behaviour in superfluid 3He; 3–5). Here we report muon spin-relaxation measurements on the superconductor Sr2RuO4 that reveal the spontaneous appearance of an internal magnetic field below the transition temperature: the appearance of such a field indicates that the superconducting state in this material is characterized by the breaking of time-reversal symmetry. These results, combined with other symmetry considerations, suggest that superconductivity in Sr2RuO4 is of ‘p-wave’ (odd-parity) type, analogous to superfluid 3He.

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Figure 1: Zero-field μSR spectra measured with Pμ ⊥ c in Sr2RuO4 at T = 2.1 K (circles) and T = 0.02 K (squares).
Figure 2: Zero-field (ZF) relaxation rate Λ for the initial muon spin polarization ∥ c (top) and ⊥ c (bottom).

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Acknowledgements

We thank K. Machida, D. Agterberg and E. M. Forgan for discussions. Research at Columbia was supported by NSF and NEDO. Y.M. and Z.Q.M. thank CREST of the Japan Science and Technology Corporation for its support.

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Authors and Affiliations

  1. Department of Physics, Columbia University, New York, 10027, New York, USA

    G. M. Luke, Y. Fudamoto, K. M. Kojima, M. I. Larkin, J. Merrin, B. Nachumi & Y. J. Uemura

  2. Department of Physics for Theoretical Physics, Kyoto University, Kyoto, 606-8502, Japan

    Y. Maeno, Z. Q. Mao & Y. Mori

  3. Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto, 606-8502, Japan

    M. Sigrist

  4. Department of Material Science and Engineering, Kyoto University, Kyoto, 606-8501, Japan

    H. Nakamura

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  1. G. M. Luke
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Correspondence to G. M. Luke.

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Luke, G., Fudamoto, Y., Kojima, K. et al. Time-reversal symmetry-breaking superconductivity in Sr2RuO4. Nature 394, 558–561 (1998). https://doi.org/10.1038/29038

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