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Magnetotransport of Sm2Ir2O7 across the pressure-induced quantum-critical phase boundary

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jats:titleAbstract</jats:title>jats:pRare-earth pyrochlore iridates host two interlocking magnetic sublattices of corner-sharing tetrahedra and can harbour a unique combination of frustrated moments, exotic excitations and highly correlated electrons. They are also the first systems predicted to display both topological Weyl semimetal and axion insulator phases. We have measured the transport and magnetotransport properties of single-crystal Smjats:sub2</jats:sub>Irjats:sub2</jats:sub>Ojats:sub7</jats:sub> up to and beyond the pressure-induced quantum critical point for all-in-all-out (AIAO) Ir order at jats:italicp</jats:italic>jats:subc</jats:sub> = 63 kbar previously identified by resonant X-ray scattering and close to which Weyl semimetallic behavior has been previously predicted. Our findings overturn the accepted expectation that the suppression of AIAO order should lead to metallic conduction persisting down to zero temperature. Instead, the resistivity-minimum temperature, which tracks the decrease in the AIAO ordering temperature for pressures up to 30 kbar, begins to increase under further application of pressure, pointing to the presence of a second as-yet unidentified mechanism leading to non-metallic behavior. The magnetotransport does track the suppression of Ir magnetism, however, with a strong hysteresis observed only within the AIAO phase boundary, similar to that found for Hojats:sub2</jats:sub>Irjats:sub2</jats:sub>Ojats:sub7</jats:sub> and attributed to plastic deformation of Ir domains. Around jats:italicp</jats:italic>jats:subc</jats:sub> we find the emergence of a new type of electronic phase, characterized by a negative magnetoresistance with small hysteresis at the lowest temperatures, and hysteresis-free positive magnetoresistance above approximately 5 K. The temperature dependence of our low-temperature transport data are found to be best described by a model consistent with a Weyl semimetal across the entire pressure range.</jats:p>


Acknowledgements: We thank T. Orton and P. Ruddy at the University of Warwick for technical assistance. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 681260). We acknowledge the Engineering and Physical Sciences Research Council (EPSRC), UK and the Oxford-ShanghaiTech collaboration project for financial support. This work was supported by EPSRC grants No. EP/P034616/1, No. EP/V062654/1 and No. EP/N034872/1. A portion of this work was performed at the National High Magnetic Field Laboratory (NHMFL), which is supported by National Science Foundation Cooperative Agreement No. DMR-1644779 and the Department of Energy (DOE). J.S. acknowledges support from the DOE BES program “Science at 100 T”, which permitted the design and construction of the specialized equipment used in the high-field studies.


5108 Quantum Physics, 51 Physical Sciences

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npj Quantum Materials

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Springer Science and Business Media LLC
Engineering and Physical Sciences Research Council (EP/P034616/1)
EPSRC (EP/V062654/1)