Dispersion of a single flux pair (odd-parity sector) for the FM (a) and AFM (b) Kitaev model for four representative perturbations indicated with black diamonds in panels (c) and (d). (c),(d) Boundaries where the single flux-pair excitation becomes soft at the wave vectors Q indicated by the colors.

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Context 1

... see in the next section, a (bosonic) bound state between a single flux pair and a matter fermion can become gapless for a lower strength of the perturbations. While more details of the instability analysis are presented in the next section, here we aim to provide a qualitative understanding of the stability of the FM or AFM Kitaev spin liquid. Fig. 7 (c) and (d) show the boundaries in the J − Γ space where the single flux-pair spectrum becomes gapless. According to this analysis, the AFM Kitaev spin liquid is more fragile against the inclusion of a Heisenberg term, while the FM Kitaev spin liquid is more fragile against the inclusion of a Gamma term. Both results are entirely consistent with ...

Context 2

... for negative Gamma interaction, multiple bands of bound states are formed and the lowest energy band has a quasi-flat dispersion. This is a direct consequence of the flat lowest energy band of a single-flux pair for the AFM Kitaev model with Γ < 0 [see Fig. 7 (b)]. For J < 0.0145|K|, the bound state becomes soft at six incommensurate wave-vectors related by the C 6 symmetry of H. These wave vectors are located on the paths that connect the M points of the Brillouin zone with the zone center or Γ point. For instance, one of these wave vectors is Q = (0, 4πq/ √ 3a) with 0 < q < 0.35. The six ...