Charge dynamics of electronic ferroelectricity in geometrically frustrated lattice

Charge dynamics in electronic ferroelectric materials, where electronic charge order is responsible for the electric polarization, is studied. Motivated from the layered iron oxide LuFe₂O₄ with a frustrated geometrical lattice, we introduce the spin-less fermion V-t model in a paired triangular lattice. This model is analyzed by utilizing the exact diagonalization method with the Lanczos algorithm in finite-size clusters. In particular, we focus on frustration effects on the charge dynamics. In the calculation of the ground state phase diagram, the non-polar two-fold charge order (CO) and the polar three-fold CO appear. In the optical conductivity spectra in the polar three-fold CO phase, multiple-peak structures appear in a wide energy range, in contrast to the spectra in the non-polar two-fold CO phase. This is originated from the non-equivalent two sublattices in the three-fold CO phase. The dynamical charge correlation function in the non-polar two-fold CO phase shows low-energy excitation at the wave vectors which correspond to the three-fold CO. This feature becomes remarkable near the phase boundary between the two-fold and three-fold CO phases. These precursor effects are attributed to the frustrated charge ordered system.