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arXiv · 2110.11588

Magnetic order, disorder, and excitations under pressure in the Mott insulator Sr$_2$IrO$_4$

Xiang Li·S. E. Cooper·A. Krishnadas·A. de la Torre·R. S. Perry·F. Baumberger·D. M. Silevitch·D. Hsieh·T. F. Rosenbaum·Yejun Feng
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Abstract

Protected by the interplay of on-site Coulomb interactions and spin-orbit coupling, Sr$_2$IrO$_4$ 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 Sr$_2$IrO$_4$ 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 $\sim$10 GPa with reduced structural anisotropy in the IrO$_6$ 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 $J_\mathrm{eff}=1/2$ pseudospins, the spin excitations are quasi-elastic and continuous to 10 meV, potentially hosting a gapless quantum spin liquid in Sr$_2$IrO$_4$.

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Xiang Li, S. E. Cooper, A. Krishnadas, A. de la Torre, R. S. Perry, F. Baumberger, D. M. Silevitch, D. Hsieh, T. F. Rosenbaum, Yejun Feng. 2021-10-22. Magnetic order, disorder, and excitations under pressure in the Mott insulator Sr$_2$IrO$_4$. https://doi.org/10.1103/physrevb.104.l201111

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