  The three-dimensional electron-gas model has been a major focus for many-body
theory applied to the electronic properties of metals and semiconductors.
Because the model neglects band effects, whereas electronic systems are
generally more strongly correlated in narrow band systems, it is most widely
used to describe the qualitative physics of weakly correlated metals with
unambiguous Fermi liquid properties. The model is more interesting in two space
dimensions because it provides a quantitative description of electrons in
quantum wells and because these can form strongly correlated many-particle
states. We illustrate the range of possible many-particle behaviors by
discussing the way correlations are manifested in 2D tunneling spectroscopy
experiments.
