Competition between spin-orbit coupling, magnetism, and dimerization in the honeycomb iridates: $\alpha$-Li${}_2$IrO${}_3$ under pressure

Abstract

Single-crystal x-ray diffraction studies with synchrotron radiation on the honeycomb iridate $\alpha$-Li${}_2$IrO${}_3$ reveal a pressure-induced structural phase transition with symmetry lowering from monoclinic to triclinic at a critical pressure of $P_c$ = 3.8 GPa. According to the evolution of the lattice parameters with pressure, the transition mainly affects the $ab$ plane and thereby the Ir hexagon network, leading to the formation of Ir--Ir dimers. These observations are independently predicted and corroborated by our \textit{ab initio} density functional theory calculations where we find that the appearance of Ir--Ir dimers at finite pressure is a consequence of a subtle interplay between magnetism, correlation, spin-orbit coupling, and covalent bonding. Our results further suggest that at $P_c$ the system undergoes a magnetic collapse. Finally we provide a general picture of competing interactions for the honeycomb lattices $A_2$$M$O${}_3$ with $A$= Li, Na and $M$ = Ir, Ru.

arXiv comment6 pages, 2 figures

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• Optical signature of the pressure-induced dimerization in the honeycomb iridate $\alpha$-Li${}_2$IrO${}_3$
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• Interplay of magnetism and dimerization in pressurized Kitaev material $\beta$-Li${}_2$IrO${}_3$
• Evidences for the random singlet phase in a new honeycomb iridate SrIr${}_2$O${}_{6-\delta }$
• Lattice dynamics and structural transition of the hyperhoneycomb iridate $\beta$-Li${}_2$IrO${}_3$ investigated by high-pressure Raman scattering
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• Dimer Crystallization Induced by Elemental Substitution in the Honeycomb Lattice of Ru1-xOsxCl3
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• Pressure-induced transition from Jeff=1/2 to S=1/2 states in CuAl2O4
• The ground state in a proximity to a possible Kitaev spin liquid: An undistorted honeycomb iridate NaxIrO3 (0.60 < x < 0.80)
• Field-Induced Ordered Phases in Anisotropic Spin-1/2 Kitaev Chains
• First-principles design of the spinel iridate Ir2O4 for high-temperature quantum spin ice
• Signatures of Floquet Engineering in the proximal Kitaev Quantum Spin Liquid H${}_3$LiIr${}_2$O${}_6$ by tr-RIXS
• Novel electronic state of honeycomb iridate Cu${}_2$IrO${}_3$ at high pressure
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• Orbital-Selective Spin-Orbit Mott Insulator in Fractional Valence Iridate La${}_3$Ir${}_3$O${}_{11}$