Abstract
Electrons in the pyrochlore iridates experience a large interaction energy in addition to a strong spin–orbit interaction. Both features make the iridates promising for realizing novel states such as the topological Mott insulator. The pyrochlore iridate Eu2Ir2O7 shows a metal–insulator transition at TN ∼ 120 K below which a magnetically ordered state develops. Using torque magnetometry, we uncover an unusual magnetic response. A magnetic field H applied in its a–b plane produces a nonlinear magnetization M⊥ orthogonal to the plane. M⊥ displays a d-wave field-angle pattern consistent with octupolar order, with a handedness dictated by field cooling, leading to symmetry breaking of the chirality ω. A surprise is that the lobe orientation of the d-wave pattern is sensitive to the direction of the field when the sample is field-cooled below TN, suggestive of an additional order parameter η already present at 300 K.
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Acknowledgements
T.L. acknowledges a scholarship from Japan Student Services Organization. N.P.O. acknowledges the support of the US National Science Foundation (Grant DMR 1420541) and the Gordon and Betty Moore Foundations EPiQS Initiative through Grant GBMF4539. L.F. and T.H.H. were supported by DOE Office of Basic Energy Sciences, DE-SC0010526. T.H.H. thanks the KITP Graduate Fellowship Program. The research at University of Tokyo is supported by grants-in-aid (no. 16H02209) and the Program for Advancing Strategic International Networks to Accelerate the Circulation of Talented Researchers (no. R2604) from JSPS, by CREST of JST, and grant-in-aid for scientific research on Innovative Areas (Grants Nos 15H05882 and 15H05883) from MEXT.
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T.L., T.H.H., L.F. and N.P.O. conceived the idea behind the experiment. T.L. designed the experiment and carried out all the measurements. T.L. and N.P.O. analysed the results with important insights from T.H.H. and L.F. The manuscript was written by T.L. and N.P.O. with numerous inputs from T.H.H. and L.F. The high-quality crystal was grown by J.J.I. and S.N. The basic characterization of crystals was made by J.J.I. and S.N. All authors discussed the results and commented on the manuscript.
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Liang, T., Hsieh, T., Ishikawa, J. et al. Orthogonal magnetization and symmetry breaking in pyrochlore iridate Eu2Ir2O7. Nature Phys 13, 599–603 (2017). https://doi.org/10.1038/nphys4051
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DOI: https://doi.org/10.1038/nphys4051
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