Magnetic order, disorder, and excitations under pressure in the Mott Insulator Sr₂IrO₄
Protected by the interplay of on-site Coulomb interactions and spin-orbit coupling, Sr₂IrO₄ at high pressure is a rare example of a Mott insulator with a paramagnetic ground state. Here, using optical Raman scattering, we measure both the phonon and magnon evolution in Sr₂IrO₄ under pressure, and identify three different magnetically-ordered phases, culminating in a spin-disordered state beyond 18 GPa. A strong first-order structural phase transition drives the magnetic evolution at ∼10 GPa with reduced structural anisotropy in the IrO₆ cages, leading to increasingly isotropic exchange interactions between the Heisenberg spins and a spin-flip transition to c-axis-aligned antiferromagnetic order. In the disordered phase of Heisenberg J_(eff) = 1/2 pseudospins, the spin excitations are quasi-elastic and continuous to 10 meV, potentially hosting a gapless quantum spin liquid in Sr₂IrO₄.
Additional Information© 2021 The Author(s). Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. (Received 7 October 2021; revised 31 October 2021; accepted 2 November 2021; published 19 November 2021) We thank G. Stenning and D. Nye for help with the instruments in the Materials Characterisation Laboratory at the ISIS Neutron and Muon Source. Y.F. acknowledges support from the Okinawa Institute of Science and Technology Graduate University, with subsidy funding from the Cabinet Office, Government of Japan. X.L., D.M.S., and T.F.R. acknowledge support from Air Force Office of Scientific Research Grant No. FA9550-20-1-0263. D.H. acknowledges support from Department of Energy Grant No. DE-SC0010533. F.B. was supported by the Swiss National Science Foundation. A.d.l.T. acknowledges support from the Swiss National Science Foundation through an Early Postdoc Mobility Fellowship (P2GEP2_165044).
Published - PhysRevB.104.L201111.pdf
Submitted - 2110.11588.pdf
Supplemental Material - SI_Sr2IrO4_Raman_10072021.pdf