Structural Stability of Sr₂IrO₄ at High Pressure: A Density Functional Theory Investigation

Sr₂IrO₄ does not show a metallic state at high pressure (up to 185 GPa) [1] unlike what would be expected for a Mott insulator. Pressure-induced structural phase transitions, which occur at multiple pressures [1--3] in this material, may explain this lack of pressure-induced metallicity. Using density functional theory, we investigated the stability of different structures of Sr₂IrO₄ as a function of pressure through both the equation of state and the phonon frequencies as calculated by finite displacement. We also investigated the effect of uniaxial stress along the c axis, and show that a structural phase transition may occur at a much lower pressure than for hydrostatic conditions.

[1] C. Chen et al., Persistent Insulating State at Megabar Pressures in Strongly Spin-Orbit Coupled Sr₂IrO₄, Phys. Rev. B 101, 144102 (2020).

[2] K. Samanta et al., First-Order Structural Transition and Pressure-Induced Lattice/Phonon Anomalies in Sr₂IrO₄, Phys. Rev. B 98, 094101 (2018).

[3] X. Li et al., Magnetic Order, Disorder, and Excitations under Pressure in the Mott Insulator Sr₂IrO₄, Phys. Rev. B 104, L201111 (2021).