Abstract
The metal–insulator transition (MIT) is a hallmark of strong correlation in solids1,2,3. Quantum MITs at zero temperature have been observed in various systems tuned by either carrier doping or bandwidth1. However, such transitions have rarely been induced by application of magnetic field, as normally the field scale is too small in comparison with the charge gap, whose size is a fraction of the Coulomb repulsion energy (∼1 eV). Here we report the discovery of a quantum MIT tuned by a field of ∼10 T, whose magnetoresistance exceeds 60,000%. In particular, our anisotropic magnetotransport measurements on the cubic insulator Nd2Ir2O7 (ref. 4) reveal that the insulating state can be suppressed by such a field to a zero-temperature quantum MIT, but only for fields near the [001] axis. The strong sensitivity to the field direction is remarkable for a cubic crystal, as is the fact that the MIT can be driven by such a small magnetic field, given the 45 meV gap energy5, which is of order of 50 times the Zeeman energy for an Ir4+ spin. The systematic change in the MIT from continuous near zero field to first order under fields indicates the existence of a tricritical point proximate to the quantum MIT. We argue that these phenomena imply both strong correlation effects on the Ir electrons and an active role for the Nd spins.
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Acknowledgements
We thank A. Matsuo for technical assistance, and K. Behnia and A. Nevidomskyy for useful discussions. This work has been supported in part by Grants-in-Aid for Scientific Research (No. 25707030), Program for Advancing Strategic International Networks to Accelerate the Circulation of Talented Researchers (No. R2604) from the Japanese Society for the Promotion of Science and PRESTO of JST, and Grant-in-Aid for Scientific Research on Innovative Areas (15H05882, 15H05883). L.B. was supported by the DOE Office of Basic Energy Sciences, DE-FG02-08ER46524. H.I. was supported by JSPS Postdoctoral Fellowships for Research Abroad. T.H.H. was supported by a KITP Graduate Fellowship and DOE Office of Basic Energy Sciences, DE-SC0010526.
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S.N. planned the experimental project. Z.T., J.J.I. and S.N. prepared single crystals. Z.T., Y.K., T.T. and K.K. performed high-field measurements. L.B. planned the theoretical project. H.I., T.H.H. and L.B. performed theoretical calculations. Z.T., T.T., L.B. and S.N. wrote the paper. T.H.H. and H.I. wrote the theory in the Supplementary Information. All authors discussed the results and commented on the manuscript.
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Tian, Z., Kohama, Y., Tomita, T. et al. Field-induced quantum metal–insulator transition in the pyrochlore iridate Nd2Ir2O7. Nature Phys 12, 134–138 (2016). https://doi.org/10.1038/nphys3567
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DOI: https://doi.org/10.1038/nphys3567
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