= Ginzburg-Landau theory
{c}
A long-wavelength order-parameter description extending a local <Landau free energy> by gradient terms. For a one-component complex field, a common isotropic form is $\mathcal F=\int[\alpha|\Psi|^2+\beta|\Psi|^4/2+K|\nabla\Psi|^2]d^3r$. A charged field instead uses a covariant gradient. Static minimization determines equilibrium profiles; a dynamical law requires additional input. <Ginzburg-Landau theory of superconductivity> and the <Ginzburg-Landau functional of a dilute Bose gas> realize this structure with different microscopic normalizations.
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