We numerically investigate the dynamical properties of κ-type molecular conductors in their antiferromagnetic Mott insulating state. By treating the extended Hubbard model on the two-dimensional κ-type lattice within the Lanzcos exact diagonalization method, we calculate the one-particle spectral function Aðk; !Þ and the optical absorption spectra taking advantage of twisted boundary conditions. We find spin splitting in Aðk; !Þ predicted by a previous Hartree–Fock study [M. Naka et al., Nat. Commun. 10, 4305 (2019)]; namely, their up- and down-spin components become different in the general k-points of the Brillouin zone, even without the spin–orbit coupling. Furthermore, we demonstrate the variation in the optical properties near the Mott gap caused by the presence or absence of the antiferromagnetic order, tuned by a small staggered magnetic field.
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