Abstract
X-ray and neutron diffraction are foundational tools for structure determination; however, their resolution limits can lead to misassignments in materials with subtle distortions. Here we demonstrate that nonlinear transport provides a powerful complementary approach to uncover hidden crystal symmetries, using Ca3Ru2O7 as a case study. Below the magnetic transition at TS = 48 K, our experiment reveals a previously overlooked lower-symmetry phase. This is evidenced by the emergence of longitudinal nonlinear resistance (NLR), indicating combined translational and time-reversal symmetry breaking, and thus rendering Ca3Ru2O7 an altermagnetic candidate in terms of symmetry classification. DFT calculation suggests that the lower-symmetry phase arises from an extremely subtle lattice distortion (~0.1 pm) below TS, below the detection limit of conventional diffraction. Moreover, NLR is accompanied by nonlinear Hall effect, both enhanced by the large quantum metric associated with Weyl chains. Our findings establish nonlinear transport as a sensitive probe of hidden symmetry breaking and highlight an alternative route to discovering altermagnetic states.
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The authors declare that all the data that support the findings of this study are available within the paper and Supplementary Information. Additional relevant data is available from the corresponding authors upon reasonable request. Source data are provided with this paper.
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Acknowledgements
This work is primarily supported by the US National Science Foundation under grant DMR 2211327. J.Z., B.H.Y. and Z.Q.M. also acknowledge the partial support from NSF through the Materials Research Science and Engineering Center DMR 2011839. Y. C. acknowledges the support of the Penn State Two-Dimensional Crystal Consortium center under grant no. NSF-DMR-2039351.
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The microscale CRO devices were fabricated by S.M. with assistance provided by Y.C., Z.L., J.Z., and Y.L. The transport measurements were conducted by S.M. and Z.M. The CRO crystals were grown by Y.W. and Z.M. The optical measurements were performed by S. S. and V.G. The theoretical work was done by Y.F.Z. and B.H.Y. The paper was written by S.M., Y.F.Z. B.H.Y., and Z.M., with input from other authors. Z.M. supervised the experimental part of this work, and B.H.Y. supervised the theoretical part.
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Mali, S., Zhao, Y., Wang, Y. et al. Probing hidden symmetry via nonlinear transport in an altermagnet candidate Ca3Ru2O7. Nat Commun (2026). https://doi.org/10.1038/s41467-026-69739-9
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DOI: https://doi.org/10.1038/s41467-026-69739-9
