ANALYSIS OF THE DC CONDUCTIVITY OF THE QUASI-ONE-DIMENSIONAL CHARGE-DENSITY-WAVE CONDUCTOR (FLUORANTHENE)(2)X

It has been shown recently that the dc conductivity (along the highly conducting axis) of fluoranthene radical cation salts exhibits the behavior of a quasi-one-dimensional conductor with a Peierls transition at about 180 K to a charge-density-wave ground state. In the high-temperature range fluctuations of the order parameter lead to a pseudogap in the electronic density of states, whereas below the phase transition the energy gap is BCS-like. To analyze the conductivity data, a simple band-structure model is used and related to optical data. In spite of the occurrence of the Peierls transition, it is assumed that three-dimensional effects and fluctuations are strong enough for the conduction to be essentially due to electron-hole transport in bands and not polaronlike. Therefore the conductivity is determined simply by the Boltzmann equation with deformation-potential scattering. (a) This model yields a good fit of experimental data using the BCS-like gap below the transition and the pseudogap as determined from paramagnetic spin susceptibility above the transition. (b) It is possible to obtain the temperature dependence of the concentration, the mobility, the relaxation time, and the mean free path of carriers. (c) One can check a fundamental criterion for the applicability of the model. (d) We obtain from the fit parameters reasonable estimates of the quantities determining the deformation-potential scattering. Moreover, it is demonstrated that the theory pan be used to determine the full temperature dependence of the gap/pseudogap directly from conductivity data,