Magnon damping in the zigzag phase of the Kitaev-Heisenberg- Γ model on a honeycomb lattice

Abstract

We calculate magnon dispersions and damping in the Kitaev-Heisenberg model with an offdiagonal exchange Γ and isotropic third-nearest-neighbor interaction J3 on a honeycomb lattice. This model is relevant to a description of the magnetic properties of iridium oxides α-Li2IrO3 and Na2IrO3, and Ru-based materials such as α-RuCl3. We use an unconventional parametrization of the spin-wave expansion, in which each Holstein-Primakoff boson is represented by two conjugate hermitian operators. This approach gives us an advantage over the conventional one in identifying parameter regimes where calculations can be performed analytically. Focusing on the parameter regime with the zigzag spin pattern in the ground state that is consistent with experiments, we demonstrate that one such region is Γ = K > 0, where K is the Kitaev coupling. Within our approach we are able to obtain explicit analytical expressions for magnon energies and eigenstates and go beyond the standard linear spin-wave theory approximation by calculating magnon damping and demonstrating its role in the dynamical structure factor. We show that the magnon damping effects in both Born and self-consistent approximations are very significant, underscoring the importance of non-linear magnon coupling in interpreting broad features in the neutron-scattering spectra. arXiv:1911.12829v1 [cond-mat.str-el]

Kitaev interactions in the Co honeycomb antiferromagnets Na3Co2SbO6 and Na2Co2Songvilay1, Robert2, Petit3 et al. 2020Phys. Rev. B968561View full textAdd to dashboardCite

“…It should be noted that our analysis was performed using a classical model, while we could expect quantum fluctuations to renormalize the excitation spectra or to cause energy and momentum broadening of the intensity, as reported in other low-dimensional frustrated magnets [54,[58][59][60][61]. Furthermore, a recent analysis of α-RuCl 3 has shown that the presence of off-diagonal terms ( and ), causing the spins to tilt out of the honeycomb plane, could induce magnon decay [40,52,62]. This effect would be expected at twice the energy of the main magnon branch and therefore could explain the discrepancies above 6 meV in both compounds, where the scattering is broad in energy and momentum.…”

Phase Diagram of YbZnGaO4 in Applied Magnetic Field

“…We also point out that an apparent visibility of the magnon modes in LSWT S (Q, ω) in the vicinity of the Γ point at low fields, Figure 3(f),(g), and lack thereof in the experimental data, Figure 3(a-c), can be explained by a significant interaction of the single-magnon branch with the two-magnon continuum. While the quantitative calculation of such effects in the anisotropic-exchange models is quite involved [51,52] and is beyond the scope of the present work, we, nevertheless, provide an intuitive insight into it by showing the bottom of the two-magnon continuum for three magnetic domains in Figure 3(f) and (g). As shown by the dashed lines in Figure 3 for both 0 T and 2.5 T, the bottom of the continuum has lower energy than one magnon modes at the large portion of the Brillouin zone, including the Γ point.…”

“…For S = 1/2 systems, such an overlap can lead to strong decays and near-complete disappearance of the well-defined magnon excitations in the corresponding range of momenta together with the other phenomena such as strong renormalization of the single-magnon branches [53,54]. These effects require significant coupling between one-and two-magnon sectors -an inevitable consequence of the anisotropic exchange terms in (1), which are allowed by the presence of strong spin-orbit coupling in the rare-earth-based and some transition-metal compounds [29,51,55].…”

Thermodynamic Perspective on Field-Induced Behavior of α−RuCl3

“…Here, we focus on α-RuCl 3 , which magnetically orders below 7 K in zero field and reveals magnon excitations at low energies [13][14][15][16][17][18]. Additionally, it shows broad high-energy spectral features that are often interpreted as fractionalized excitations -vestiges of the proximate QSL state [13,[19][20][21][22] -although this behavior can also be described in terms of magnon decays and incoherent excitations originating from strong magnetic anharmonicities [23][24][25][26]. In-plane magnetic fields lead to a gradual suppression of magnetic order that completely disappears around B AF2 c 7.5 T [27][28][29][30][31] (see also the inset of Fig.…”