Landau theory

Summary

Landau theory describes a continuous phase transition by a free energy that is a polynomial in the order parameter. The coefficients depend on the temperature, and the terms allowed are those invariant under the symmetry of the system. The equilibrium value of the order parameter is the point where this free energy is minimal. The theory predicts the mean-field critical exponents, and with a gradient term it becomes the Ginzburg–Landau theory.