The effect of Coulomb interactions on the ac mobility of charges in quasi-one-dimensional systems. Example: discotic liquid crystals

Using Monte Carlo simulations we calculate the frequency dependence of the diffusive mobility of a group of carriers on a short one-dimensional chain. We allow the carriers to interact with each other through weakly screened long-range Coulomb potentials. We consider both doped systems with discrete immobile counterions and gated systems with constant neutralizing background. In doped systems the counterions can act as traps for the mobile charge, which results in a strong frequency-dependent conductivity. In the gated charged system, the mobility per particle decreases with particle density. The calculations show that the electron–electron interaction, in the diffusion limit, acts very much like a source of random disorder. Because the mobility depends on the number of carriers, arrays of coupled wires can exhibit current “noise” which is directly related to charge exchange between the wires. This noise is in principle observable in signal processing. Basing ourselves on our numerical results, we have been able to conclude that the low-frequency ac mobility measured in doped triphenylenes must be due to spatial charge inhomogeneities, and cannot be due to intrinsic charge dynamics