Noncubic local distortions and spin-orbit excitons in K2 IrCl6
- Authors
- Lee, Seungyeol; Kim, Beom Hyun; Seong, Maeng-Je; Choi, Kwang-Yong
- Issue Date
- May-2022
- Publisher
- American Physical Society
- Citation
- Physical Review B, v.105, no.18
- Journal Title
- Physical Review B
- Volume
- 105
- Number
- 18
- URI
- https://scholarworks.bwise.kr/cau/handle/2019.sw.cau/58308
- DOI
- 10.1103/PhysRevB.105.184433
- ISSN
- 2469-9950
2469-9969
- Abstract
- The cubic antifluorite K2IrCl6 has recently garnered renewed attention due to its relevance to Kitaev magnetism. Combining Raman spectroscopy with numerical calculations, we investigate its electronic structure and ensuing low-lying excitations as well as lattice instabilities. For temperatures below T∗≈180 K, we observe several lattice anomalies: (i) a gradual appearance of the symmetry-forbidden phonons; (ii) a central-mode-like excitation; and (iii) a soft-mode-like behavior of the Γ5+ mode involving vibrations of the K+ ion relative to the Cl- ion. All these features indicate the occurrence of local noncubic distortions. At high energies, we observe spin-orbit (SO) excitons made of five peaks at ω=0.62-0.79 eV as well as a weak electronic excitation at ω=0.12-0.86 eV. Our numerical calculations reproduce their spectral energy and shape with the electronic parameters: SO coupling λ=465 meV; Hund's coupling JH=300 meV; tetragonal distortion strength Δt=30 meV and on-site Coulomb interaction U=2.2 eV. The multiple SO excitons are interpreted in terms of bounded SO excitons of the |jeff=32,±12) states arising from the coupling between the SO excitons and electron-hole excitations. Our results showcase that K2IrCl6 is on the brink of a structural phase transition. © 2022 American Physical Society.
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