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

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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Cited by in corpus (3)

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• Strain-induced superconductivity in Sr2IrO4
• Observation of excitons bound by antiferromagnetic correlations