Fig. 6. Theoretical exchange parameters.

Exchange parameters K (red), J (black), Γ (blue), and ${\mathrm{\Gamma }}^{\prime }$ (gray) as a function of δ = 2Δ/λ, calculated using 10Dq = 2.4 eV, J_H = 0.34 eV, and the pd charge-transfer gap Δ_pd = 5.5 eV as obtained from the RIXS data (Fig. 2). We use representative values of the Coulomb interaction U = 2.5 eV for the Ru-d orbitals, U_p = 1.5 eV and Hund’s coupling J_p = 0.7 eV for the Cl-p orbitals, a ratio of t_pdσ/t_pdπ = 2 between the pd charge-transfer integrals in the σ and π channels, and a direct t_2g hopping $t^{\prime }=0.4t$. The exchange constants are given in units of t²/U. The vertical gray line indicates δ ~ − 0.7 appropriate for RuCl₃.