eprintid: 10185457 rev_number: 6 eprint_status: archive userid: 699 dir: disk0/10/18/54/57 datestamp: 2024-01-16 11:43:34 lastmod: 2024-01-16 11:43:34 status_changed: 2024-01-16 11:43:34 type: article metadata_visibility: show sword_depositor: 699 creators_name: Saheli, Shahnam Ghanbari creators_name: Lin, Jennifer creators_name: Hu, Huanzhi creators_name: Krüger, Frank title: Majorana-fermion mean field theories of Kitaev quantum spin liquids ispublished: pub divisions: UCL divisions: B04 divisions: C06 divisions: F60 divisions: F64 note: © 2024 American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0/). abstract: We determine the phase diagrams of anisotropic Kitaev-Heisenberg models on the honeycomb lattice using parton mean-field theories based on different Majorana fermion representations of the S = 1/2 spin operators. First, we use a two-dimensional Jordan-Wigner transformation (JWT) involving a semi-infinite snake string operator. To ensure that the fermionized Hamiltonian remains local, we consider the limit of extreme Ising exchange anisotropy in the Heisenberg sector. Second, we use the conventional Kitaev representation in terms of four Majorana fermions subject to local constraints, which we enforce through Lagrange multipliers. For both representations, we self-consistently decouple the interaction terms in the bond and magnetization channels and determine the phase diagrams as a function of the anisotropy of the Kitaev couplings and the relative strength of the Ising exchange. While both mean-field theories produce identical phase boundaries for the topological phase transition between the gapless and gapped Kitaev quantum spin liquids, the JWT fails to correctly describe the magnetic instability and finite-temperature behavior. Our results show that the magnetic phase transition is first order at low temperatures but becomes continuous above a certain temperature. At this energy scale, we also observe a finite-temperature crossover on the quantum-spin-liquid side, from a fractionalized paramagnet at low temperatures, in which gapped flux excitations are frozen out, to a conventional paramagnet at high temperatures. date: 2024-01 date_type: published publisher: American Physical Society (APS) official_url: http://dx.doi.org/10.1103/physrevb.109.014407 oa_status: green full_text_type: pub language: eng primo: open primo_central: open_green verified: verified_manual elements_id: 2139450 doi: 10.1103/physrevb.109.014407 lyricists_name: Hu, Huanzhi lyricists_name: Kruger, Frank lyricists_id: HHUAX88 lyricists_id: FKRUG35 actors_name: Kruger, Frank actors_id: FKRUG35 actors_role: owner full_text_status: public publication: Physical Review B volume: 109 number: 1 article_number: 014407 citation: Saheli, Shahnam Ghanbari; Lin, Jennifer; Hu, Huanzhi; Krüger, Frank; (2024) Majorana-fermion mean field theories of Kitaev quantum spin liquids. Physical Review B , 109 (1) , Article 014407. 10.1103/physrevb.109.014407 <https://doi.org/10.1103/physrevb.109.014407>. Green open access document_url: https://discovery.ucl.ac.uk/id/eprint/10185457/1/KitaevIsing.pdf