2018/02/28 by Takafumi Suzuki, Sei-ichiro Suga
Engineering · Physics and Astronomy · #Ab initio #Advanced Condensed Matter Physics #Condensed matter physics #Heat capacity #Inelastic neutron scattering #Machine learning #Neutron scattering #Perovskite Materials and Applications #Physics #Physics of Superconductivity and Magnetism #Quantum mechanics #Scattering #Spin (aerodynamics) #Thermodynamics #cond-mat.str-el #k-nearest neighbors algorithm
paper · pdf · doi:10.1103/physrevb.97.134424
published as Phys. Rev. B 97, 134424 (2018) · 12 pages and 9 figures. v2 : published version. Discussions for Raman spectra have been added. The numerical results for model 2 have been corrected by using the adequate parameters
openalex publication_date 2018/04/25 · openalex created_date 2018/05/07 · arxiv created 2019/06/06 · arxiv updated 2019/06/07 · openalex updated_date 2026/08/05
We use an exact numerical diagonalization method to calculate the dynamical spin structure factors of three ab initio models and one ab initio guided model for a honeycomb-lattice magnet \ensuremathα\text\ensuremath-RuCl3. We also use thermal pure quantum states to calculate the temperature dependence of the heat capacity, the nearest-neighbor spin-spin correlation function, and the static spin structure factor. From the results obtained from these four effective models, we find that, even when the magnetic order is stabilized at low temperature, the intensity at the \mathrm\ensuremathΓ point in the dynamical spin structure factors increases with increasing nearest-neighbor spin correlation. In addition, we find that the four models fail to explain heat-capacity measurements whereas two of the four models succeed in explaining inelastic-neutron-scattering experiments. In the four models, when temperature decreases, the heat capacity shows a prominent peak at a high temperature where the nearest-neighbor spin-spin correlation function increases. However, the peak temperature in heat capacity is too low in comparison with that observed experimentally. To address these discrepancies, we propose an effective model that includes strong ferromagnetic Kitaev coupling, and we show that this model quantitatively reproduces both inelastic-neutron-scattering experiments and heat-capacity measurements. To further examine the adequacy of the proposed model, we calculate the field dependence of the polarized terahertz spectra, which reproduces the experimental results: the spin-gapped excitation survives up to an onset field where the magnetic order disappears and the response in the high-field region is almost linear. Based on these numerical results, we argue that the low-energy magnetic excitation in \ensuremathα\text\ensuremath-RuCl3 is mainly characterized by interactions such as off-diagonal interactions and weak Heisenberg interactions between nearest-neighbor pairs, rather than by the strong Kitaev interactions.