Introduction to Highly Conducting One-Dimensional Solids

In the past several years a number of materials, such as K2Pt(CN)4X0.3·xH2O, X = Cl, Br (KCP), the tetracyanoquinodimethane (TCNQ) salts, and the sulfur-nitrogen polymer [(SN)x], have been discovered whose microscopic structure consists, to a greater or lesser extent, of a collection of weakly coupled, highly conducting chains. Such materials are called quasi-one-dimensional metals and they are of interest because nearly one-dimensional metals are expected to exhibit unusual collective behavior such as the Peierls instability and various kinds of superconductivity. The purpose of this chapter is to provide an entry point into the subject of quasi-one-dimensional conductors, by defining the terms, introducing the most important arguments, and raising some of the questions that will be discussed in the following chapters.