Landau theory expands an effective free energy analytically in powers of an order parameter, constrained by symmetry.
Landau-Ginzburg theory supplements the local Landau potential with gradient terms and treats the order parameter as a spatial field.
For an ordinary quartic Landau transition, the heat-capacity and order-parameter exponents are and . At a tricritical sextic point they are and .
A tricritical point is where a line of continuous transitions meets a line of first-order transitions; in a Landau expansion both quadratic and quartic coefficients vanish and a positive sextic term stabilizes the free energy.
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Landau theory, often referred to as Landau's theory of phase transitions, is a framework developed by the Soviet physicist Lev Landau in the early 20th century to describe phase transitions in physical systems. It provides a mathematical formalism for understanding how a system changes from one phase to another, typically as a function of temperature or other external parameters.