Landau theory

Landau theory (also known as Ginzburg–Landau theory (GL), and Ginzburg–Landau-Devonshire theory (GLD), despite the confusing names) in physics is a theory that Lev Landau (and Vitaly Ginzburg and Albert Frederick Devonshire) introduced in an attempt to formulate a general theory of continuous (i.e., second-order) phase transitions. It can also be adapted to systems under externally-applied fields, and used as a quantitative model for discontinuous (i.e., first-order) transitions. Although the theory has now been superseded by the renormalization group and scaling theory formulations, it remains an exceptionally broad and powerful framework for phase transitions, and the associated concept of the order parameter as a descriptor of the essential character of the transition has proven transformative.