Collective excitations in layered organic conductors

We apply the dielectric formalism within random phase approximation (RPA) and G(0)W(0) approximation to the tight-binding multi-band systems with the three-dimensional long-range Coulomb interaction in order to calculate the one-particle spectral function for TTF-TCNQ and to investigate dielectric properties of quasi-two-dimensional conductor beta ''-(BEDT-TTF)(2)SF(5)CH(2)CF(2)SO(3) In the model with two one-dimensional electron bands per donor and acceptor chains appropriate for TTF-TCNQ the RPA dielectric response comprises a low energy collective mode due to the strong coupling between the plasmon and the dipolar modes together with the mode at order of magnitude higher energies The first mode is responsible for the absence of low-energy quasi-particles and the appearance of broad dispersion at low energies in the spectral function The wide structure at higher energies is due the second mode These results are in the qualitative agreement with the ARPES data In the model with two conducting bands one one-dimensional and the other two-dimensional which can be applied to beta ''-(BEDT-TTF)(2)SF(5)CH(2)CF(2)SO(3) the coupling between the plasmon and the dipolar mode leads to the appearance of the low energy collective mode perpendicular to the stacks while the low energy dipolar mode persists along the stacks as is observed in optical measurements (C) 2009 Elsevier B V All rights reserved