Pressure-induced structural dimerization in the hyperhoneycomb iridate $\beta \text{-}\mathrm{Li}{}_2\mathrm{IrO}{}_3$ at low temperatures

Journal Article · 21 August 2019 · Physical Review B

DOI: https://doi.org/10.1103/PhysRevB.100.064104 · OSTI ID:1574949

Veiga, L. S. I.  ^[1]; Glazyrin, K. ^[2]; Fabbris, G. ^[3]; Dashwood, C. D. ^[1]; Vale, J. G. ^[1]; Park, H. ^[4]; Etter, M. ^[2]; Irifune, T. ^[5]; Pascarelli, S. ^[6]; McMorrow, D. F. ^[1]; Takayama, T. ^[7]; Takagi, H. ^[7]; Haskel, D. ^[3]

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1. Univ. College London, Bloomsbury (United Kingdom)
2. Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
3. Argonne National Lab. (ANL), Argonne, IL (United States)
4. Univ. of Illinois, Chicago, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
5. Ehime Univ., Matsuyama (Japan); Tokyo Institute of Technology (Japan)
6. European Synchrotron Radiation Facility (ESRF), Grenoble (France)
7. Max Planck Inst. for Solid State Research, Stuttgart (Germany); Univ. of Tokyo (Japan)

A pressure-induced collapse of magnetic ordering in β-Li₂IrO₃ at P_m similar to 1.5-2 GPa has previously been interpreted as evidence for potential emergence of spin liquid states in this hyperhoneycomb iridate, raising prospects for experimental realizations of the Kitaev model. Based on structural data obtained at room temperature, this magnetic transition is believed to originate in small lattice perturbations that preserve crystal symmetry, and related changes in bond-directional anisotropic exchange interactions. In this work, we report on the evolution of the crystal structure of β-Li₂IrO₃ under pressure at low temperatures (T ≤ 50 K) and show that the suppression of magnetism coincides with a change in lattice symmetry involving Ir-Ir dimerization. The critical pressure for dimerization shifts from 4.4(2) GPa at room temperature to similar to 1.5-2 GPa below 50 K. While a direct Fddd → C-2/c transition is observed at room temperature, the low temperature transitions involve new as well as coexisting dimerized phases. Additional investigation of the Ir (L₃/L₂) isotropic branching ratio in x-ray absorption spectra indicates that the previously reported departure of the electronic ground state from a J_eff = 1/2 state is closely related to the onset of dimerized phases. In essence, our results suggest that the predominant mechanism driving the collapse of magnetism in β-Li₂IrO₃ is the pressure-induced formation of Ir₂ dimers in the hyperhoneycomb network. The results further confirm the instability of the J_eff = 1/2 moments and related noncollinear spiral magnetic ordering against formation of dimers in the low-temperature phase of compressed β-Li₂IrO₃.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1574949
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 6 Vol. 100; ISSN 2469-9950; ISSN PRBMDO
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English