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Free keywords:
Dispersions; Electric fields; Honeycomb structures; Paramagnetism; Topology; Anti-symmetric; Crystalline electric fields; Exciton dispersion; F-electrons; Honeycomb lattices; Inter-site exchange; Localised; Paramagnetic state; Symmetrics; Symmetry analysis; Excitons
Abstract:
We investigate the dispersive paramagnetic excitons on the honeycomb lattice that originate from the crystalline electric field split localized f-electron states in the paramagnetic state due to intersite exchange. We start with a symmetry analysis of possible Ising-type singlet-singlet and xy-type singlet-doublet models. The former supports only symmetric intersite exchange while the latter additionally allows for antisymmetric Dzyaloshinski-Moriya exchange interactions. We calculate the closed expressions for magnetic exciton dispersion using both response function formalism and bosonic Bogoliubov approach. We do this for the most general model that shows inversion-symmetry breaking on the honeycomb lattice but also discuss interesting special cases. By calculating Berry curvatures and Chern numbers of paramagnetic excitons we show that the xy model supports nontrivial topological states in a wide range of parameters. This leads to the existence of excitonic topological edge states with Dirac dispersion lying in the zone boundary gap without the presence of magnetic order. © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.
