Temperature dependence of the charge carrier mobility in gated quasi-one-dimensional systems

The many-body Monte Carlo method is used to evaluate the frequency-dependent conductivity and the average mobility of a system of hopping charges, electronic or ionic, on a one-dimensional chain or channel of finite length. Two cases are considered: the chain is connected to electrodes and in the other case the chain is confined, giving zero dc conduction. The concentration of charge is varied using a gate electrode. At low temperatures and with the presence of an injection barrier, the mobility is an oscillatory function of density. This is due to the phenomenon of charge density pinning. Mobility changes occur due to the cooperative pinning and unpinning of the distribution. At high temperatures, we find that the electron-electron interaction reduces the mobility monotonically with density, but perhaps not as much as one might intuitively expect because the path summation favor the "in-phase contributions" to the mobility, i.e., the sequential paths in which the carriers have to wait for the one in front to exit and so on. The carrier interactions produce a frequency-dependent mobility which is of the same order as the change in the dc mobility with density; i.e., it is a comparably weak effect. However, when combined with an injection barrier or intrinsic disorder, the interactions reduce the free volume and amplify disorder by making it nonlocal, and this can explain the too early onset of frequency dependence in the conductivity of some high mobility quasi-one-dimensional organic materials.