Charge and dielectric response to terahertz pulses in the charge-ordered phase of α−(BEDT−TTF)2I3

Abstract

We investigated the dielectric properties of the charge-ordered phase of $\ensuremath{\alpha}\ensuremath{-}{(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF})}_{2}{\mathrm{I}}_{3}$ using exact numerical calculations of an extended Hubbard model. The electronic contribution to the electric polarization (electronic polarization) $\overline{\mathbit{P}}$ of the charge-ordered ground state is obtained by directly calculating the current when transfer integrals were changed adiabatically from symmetric integrals to integrals for the charge-ordered phase without inversion symmetry. The angle of $\overline{\mathbit{P}}$ from the positive $b$ axis is ${36}^{\ensuremath{\circ}}$, which is consistent with experimental results and previous theoretical results based on density-functional theory. Furthermore, we numerically calculated the dynamics induced by terahertz- (THz-) pulse excitation. Both the THz-pulse-induced variation of the electronic polarization magnitude and that of the charge disproportionation that shows the charge-order amplitude are largest when the electric field of the THz pulse and $\overline{\mathbit{P}}$ have almost the same direction. This originates from the charge transfer through bond $b{2}^{\ensuremath{'}}$ being dominant in both the adiabatic flow of the current and the THz-pulse excitation. These results reproduce important features of the experimental results of THz-pulse-induced dynamics.