Commensurate-incommensurate conduction in quasi-one-dimensional organic systems

The commensurability dependence of conduction in one-dimensional systems has been studied. A new umklapp scattering mechanism is proposed in the commensurate phase which causes a quenching of the 2kF phonon flow. It is shown that this quenching mechanism accounts quantitatively for the following observed features: (i) the difference between the conductivity of tetrathiafulvalene tetracyanoquinodimethane (TTF-TCNQ) in the commensurate and incommensurate phase, (ii) the temperature dependence of, (iii) the pressure dependence of, which explains why the observed for tetraselenofulvalene (TSF)-TCNQ is small, (iv) the commensurability width, and (v) the difference in the effect of commensurability on the conductivity perpendicular to the chains and along the chains. Comparison is made between the present theory and the sliding charge-density-wave contribution to the conductivity.