Role of interchain coupling in linear conductors

Renormalization-group methods are applied to a set of coupled linear chains in a model in which direct hopping between chains is excluded. Attention is focused on models in which intrachain interactions are repulsive. It is shown first for two chains and then for N chains that a repulsive δ-function intrachain interaction scales with decreasing temperature to the attractive fixed point. In the N-chain model this attractive fixed point is characterized by a charge-density wave whose phase is coherent between chains. A variety of response functions, spin and charge density wave at wave vector 2kF (kF is the Fermi wave vector), and excitonic response functions are calculated numerically. We also evaluate the uniform magnetic susceptibility and the charge-density-wave response at 4kF. A comparison is made to the behavior of TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane) at temperatures above 60 K. It is possible to qualitatively explain most of the behavior of this compound by assuming strong repulsion between electrons. A simple physical discussion of the strong-repulsion limit is given.