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

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• Dr. Matthew Coak, London Centre for Nanotechnology, University College London
• Wednesday 23 November 2022, 11:15-12:30
• Mott Seminar Room (531), Cavendish Laboratory, Department of Physics.

If you have a question about this talk, please contact Malte Grosche.

The family of rare-earth pyrochlore iridates Ln2Ir2O7 comprise an ideal environment for investigating fundamental magnetism and correlated-electron physics. In addition to the all-in-all-out (AIAO) magnetism of the Ir ions, and associated metal-insulator transition, the rare-earth sublattice in these materials may also show interesting and correlated behavior. In Dy2Ir2O7 and Ho2Ir2O7, the large rare-earth Ising moments are constrained along their local [111] axes and are coupled ferromagnetically via dipolar interactions, promoting spin-ice physics and the appearance of magnetic monopole quasiparticles. I will first discuss our ambient-pressure measurements of magnetotransport under different orientations at Warwick, and their explanation in terms of a magnetic monopole density, before moving on to discuss the Samarium compound. We have measured the transport and magnetotransport properties of single-crystal Sm2Ir2O7 for the first time, then tuned them up to and beyond the pressure-induced quantum critical point for AIAO Ir order suppression at pc = 63 kbar previously identified by resonant X-ray scattering. Contrary to prior predictions, we do not find a crossover from insulating to metallic behavior at low temperatures above pc. Instead, the metal-insulator transition 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 an additional localization mechanism. The behavior of magnetotransport does track the Ir magnetism, however, with a strong hysteresis observed only within the AIAO phase boundary, similar to that found for Ho2Ir2O7 and attributed to plastic deformation of Ir domains. Around pc a new type of electronic behavior emerges, characterized by negative magnetoresistance with small hysteresis at the lowest temperatures, and hysteresis-free positive magnetoresistance above 5 K. The results are discussed in light of the Weyl semimetal and quadratic-band-touching phases predicted to occur in the vicinity of the quantum critical point.

This talk is part of the Quantum Matter Seminar series.

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