Interchain coupling in linear conductors

Abstract

The authors study the model of a quasi-one-dimensional metal in which the interaction of conduction electrons with intra-molecular modes and three-dimensional acoustic phonons generates two energy scales: the gap in the electron spectrum Delta and the temperature of the structural transition Tc. Tc proves to be the parameter determining the main properties of the system. An expansion in powers of the lattice deformation shows that the mean-field theory has no region of applicability in the system under study. Below the structural transition point there appears an optically active Frolich mode. In the case of compounds with two oppositely charged chains the frequency of this mode turns out to be of the order Tc. One further low-frequency optically active mode is found in the system under study. It corresponds to electron density excitations and has a gap approximately Tc. In the model considered, unlike the Peierls model, there is no adiabatic parameter and both modes result in the dielectric constant epsilon approximately omega 02/Tc2, where omega 0 is the plasma frequency.