Coulomb Effects in Low-Dimensional Systems.

In general, low-dimensional systems show relatively strong Coulomb effects than in three dimensions. In the present article, we consider such effects by choosing three different examples. Although the problems in these examples are different from each other, we shall make a somewhat unified approach with some appropriate individual modifications. These examples have been taken from two well known systems: First, electrons in a conducting polymer TTF-TCNQ as a typical one-dimensional system, second, electrons in Si inversion layers or at semiconductor interfaces. In the former case, the electrons move in the direction of strands, and in the second case electrons move more or less freely in the interface plane. These actual electron systems involve impurity and other complications. For analytical approaches, we shall concentrate in Coulomb effects neglecting these complications. Even so, there is an intrinsic many electron problem which makes, for example, low density treatments very difficult. Keeping such a theoretical limitation in mind, we shall present some basic treatments of these systems and elucidate the current theoretical status with some new results.