Antiferromagnetic State in $\kappa$-type Molecular Conductors: Spin Splitting and Mott Gap

TL;DR

This study uses numerical methods to analyze the antiferromagnetic Mott insulating state in $ppa$-type molecular conductors, revealing spin splitting in spectral functions and effects on optical properties without spin-orbit coupling.

Contribution

It provides the first numerical confirmation of spin splitting in spectral functions of $ppa$-type conductors and explores how antiferromagnetic order influences optical spectra.

Findings

Spin splitting in spectral functions confirmed numerically.

Optical properties vary with antiferromagnetic order.

Spin components differ across the Brillouin zone without spin-orbit coupling.

Abstract

We numerically investigate the dynamical properties of $\kappa$-type molecular conductors in their antiferromagnetic Mott insulating state. By treating the extended Hubbard model on the two-dimensional $\kappa$-type lattice within the Lanzcos exact diagonalization method, we calculate the one-particle spectral function $A(\boldsymbol{k}, \omega)$ and the optical absorption spectra taking advantage of twisted boundary conditions. We find spin splitting in $A(\boldsymbol{k}, \omega)$ 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 $\boldsymbol{k}$-points of the Brillouin zone, even without the spin-orbit coupling. Furthermore, we demonstrate the variation in the optical properties near the Mott gap by the presence or absence of the antiferromagnetic order, tuned by a small staggered magnetic field.