We have already mentioned that the electron gas in metals is formed by electrons that participate in conductivity. This description of a metal is, of course, casual and has the following significant short-coming. Particles of an ideal gas do not interact with each other at all. The simplest way to have an idea of the interaction in a gas is to consider a model of billiard balls that may collide but do not affect the position of each other in any other way. This consideration alone is sufficient to understand some phenomena, and, for this reason, we applied it in the first chapter of this book.

But in fact, particles of an electron gas are charges and interact with each other according to Coulomb s law. It would be more correct to compare them with a liquid. L.D.Landau used to say in this connection: Nobody has abrogated Coulomb s law . So he employed the notion of a liquid to create the Fermi-liquid theory of electrons in metals.

The liquid takes an intermediate position between the gas and the solid. Gas particles are far from one another and they are almost independent. Particles of a liquid are closer; they already feel each other and their interaction is sufficient to keep them together but insufficient for them to take stable positions in the crystal lattice sites in a solid.

Well, let us regard conduction electrons in a metal as an electron liquid and compare the current with liquid flow rather...