The subject of the electron glass has been evolving from a number of different directions so the terminology in the literature is not uniform. Fleishman and Anderson (1980) first referred to a system of disorder-localized electrons with Coulomb interactions as Fermi glass. Subsequently the term was used for noninteracting Anderson-localized electrons while in the presence of interactions such systems became known in a broad sense as the electron glass (or sometimes Coulomb glass), and it is used in this way here. Sometimes the term is used more narrowly referring to materials with localized interacting electrons exhibiting the glassy properties described in Chapter 7.

The complications resulting from the need to include disorder, interactions, and in many cases quantum effects necessitated a number of approximations to facilitate a solution and an understanding of the properties of the electron glass, whether analytically or by computer simulations. Both methods have been amply employed. In the final count, the success or failure of the theory must be evaluated according to how well predictions agree with experiment.

A proper description of the electron glass must contain the disorder that is localizing the states and the poorly screened Coulomb interactions. The combined effect of disorder and interactions is bound to produce frustration (see Chapter 3), which is often considered to be the key ingredient to glassiness.

The dynamics of disordered systems with localized wave functions are usually slow, since the motion of their particles is by hopping rather than by diffusion, characteristic of systems with extended states.