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Ligand field luminescence in the honeycomb Mott insulator α-RuCl3

Mandal, S and Banerjee, A and Ganesan, R and Kumar, PSA (2023) Ligand field luminescence in the honeycomb Mott insulator α-RuCl3. In: New Journal of Physics, 25 (5).

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Official URL: https://doi.org/10.1088/1367-2630/acd5ab


Novel electronic structure is central to Kitaev-like quantum spin liquid ground state in the van der Waals antiferromagnet α-RuCl3. In this octahedral low-spin 4 d 5 system, the rich bandstructure includes Mott-Hubbard insulating bandgap of ∼1.1 eV and ligand field induced gap of ∼2 eV. Though the bandgap is extensively reported in previous optical and photoemission studies, the latter gap is less understood. In this regard, we probed the ligand field-induced electronic structure of bulk α-RuCl3 single crystals via unpolarized photoluminescence (PL) spectroscopy under linearly polarized excitation in the visible region. We observed the broad principal PL peak at E PL ≈ 1.87 eV, close to the energy required for the optical transition across the ligand field splitting gap (∼2 eV). This gap (E PL) monotonically increases with temperature, described by the thermal expansion of lattice parameters dominating the electron-phonon interaction in this Honeycomb Mott insulator. Moreover, we observed the multiplet structure of the PL spectra, which can be explained by parity-forbidden d-d transitions in the light of single ion ligand-field theory. We attribute the broad PL linewidths to strong vibronic coupling modeled by the Huang-Rhys parameter. Further we observed the signature of structural transitions, indicated by thermal hysteresis in normalized integrated PL intensity.

Item Type: Journal Article
Publication: New Journal of Physics
Publisher: Institute of Physics
Additional Information: The copyright for this article belongs to the author.
Keywords: Kitaev-like quantum spin liquid; mott insulator; photoluminescence
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 14 Jul 2023 06:17
Last Modified: 14 Jul 2023 06:17
URI: https://eprints.iisc.ac.in/id/eprint/82394

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