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Published June 1, 2020 | Submitted + Published + Supplemental Material
Journal Article Open

Approaching the quantum critical point in a highly-correlated all-in-all-out antiferromagnet


Continuous quantum phase transition involving all-in–all-out (AIAO) antiferromagnetic order in strongly spin-orbit-coupled 5d compounds could give rise to various exotic electronic phases and strongly-coupled quantum critical phenomena. Here we experimentally trace the AIAO spin order in Sm₂Ir₂O₇ using direct resonant x-ray magnetic diffraction techniques under high pressure. The magnetic order is suppressed at a critical pressure P_c=6.30GPa, while the lattice symmetry remains in the cubic Fd−3m space group across the quantum critical point. Comparing pressure tuning and the chemical series R₂Ir₂O₇ reveals that the approach to the AIAO quantum phase transition is characterized by contrasting evolutions of the pyrochlore lattice constant a and the trigonal distortion surrounding individual Ir moments, which affects the 5d bandwidth and the Ising anisotropy, respectively. We posit that the opposite effects of pressure and chemical tuning lead to spin fluctuations with different Ising and Heisenberg character in the quantum critical region. Finally, the observed low pressure scale of the AIAO quantum phase transition in Sm₂Ir₂O₇ identifies a circumscribed region of P-T space for investigating the putative magnetic Weyl semimetal state.

Additional Information

© 2020 American Physical Society. Received 11 October 2019; revised manuscript received 13 May 2020; accepted 15 May 2020; published 4 June 2020. We are grateful to Y. Ren for discussions. Y.F. acknowledges support from Okinawa Institute of Science and Technology Graduate University with subsidy funding from the Cabinet Office, Government of Japan. The work at Caltech was supported by National Science Foundation Grant No. DMR-1606858. The work in Oxford was supported by U.K. Engineering and Physical Sciences Research Council Grant No. EP/N034872/1. The work at the Advanced Photon Source of Argonne National Laboratory was supported by the U.S. Department of Energy Basic Energy Sciences under Contract No. DE-AC02-06CH11357.

Attached Files

Published - PhysRevB.101.220404.pdf

Submitted - 1912.11640.pdf

Supplemental Material - Supplementary_materials.04202020.pdf


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