The recent discovery of high-temperature superconductors and that of
quasicrystals have underlined the importance of theories that are able to
account for the physical properties, including the phase transitions, of
materials that are inherently complex for chemical or structural reasons. This
volume discusses examples of such theories and theoretical models that are
applicable to two classes of such materials: the heavy fermion (or heavy electron)
metals, so named because of their extraordinarily large electron effective
masses, and modulated structures that have magnetic or structural
modulations superimposed on the underlying three-dimensional periodic
structure. These modulations can be commensurate or incommensurate with
the basic units and may have arbitrarily long wavelengths.