Pressure-induced collapse of the spin-orbital Mott state in the hyperhoneycomb iridate β-Li2IrO3

T. Takayama*, A. Krajewska, A. S. Gibbs, A. N. Yaresko, H. Ishii, H. Yamaoka, K. Ishii, N. Hiraoka, N. P. Funnell, C. L. Bull, H. Takagi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)

Abstract

Hyperhoneycomb iridate β-Li2IrO3 is a three-dimensional analog of two-dimensional honeycomb iridates, such as α-Li2IrO3, which recently appeared as another playground for the physics of Kitaev-type spin liquid. β-Li2IrO3 shows a noncollinear spiral ordering of spin-orbital-entangled Jeff = 1/2 moments at low temperatures below 38 K, which is known to be suppressed under a pressure of similar to ∼2 GPa. In addition, a structural transition is observed at Ps ∼ 4 GPa at room temperature. Using the neutron powder diffraction technique, the crystal structure in the high-pressure phase of β-Li2IrO3 above PS was refined, which indicates the formation of Ir2 dimers on the zigzag chains, with an Ir-Ir distance of ∼ 2.66 Å, even shorter than that of metallic Ir. We argue that the strong dimerization stabilizes the bonding molecular-orbital state comprising the two local dzx, orbitals in the Ir-O2 -Ir bond plane, which conflicts with the equal superposition of dxy, dyz, and dzx, orbitals in the Jeff = 1/2 wave function produced by strong spin-orbit coupling. The results of resonant inelastic x-ray scattering measurements and the electronic structure calculations are fully consistent with the collapse of the Jeff = 1/2 state. The competition between the spin-orbital-entangled Jeff = 1/2 state and molecular-orbital formation is most likely universal in honeycomb-based Kitaev materials.

Original languageEnglish
Article number125127
Number of pages7
JournalPhysical Review B
Volume99
Issue number12
DOIs
Publication statusPublished - 15 Mar 2019

Keywords

  • Electronic structure
  • Pressure effects
  • Spin liquid
  • Spin-orbit coupling
  • Iridates
  • Resonant inelastic x-ray scattering

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