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

We investigated the dielectric properties of the charge-ordered phase of alpha-(BEDT-TTF)(2)I-3 using exact numerical calculations of an extended Hubbard model. The electronic contribution to the electric polarization (electronic polarization) (P) over bar 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 (P) over bar from the positive b axis is 36 degrees, 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 (P) over bar have almost the same direction. This originates from the charge transfer through bond b2' 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.