Landau theory

About: Landau theory is a research topic. Over the lifetime, 2882 publications have been published within this topic receiving 57078 citations.

Spin Fluctuations in Itinerant Electron Systems

Abstract: Spin fluctuations are introduced to describe the finite temperature properties of itinerant electron ferromagnets To this end it is shown how Gaussian fiuctuations of the magnetic moment can be included in a Landau type free energy expansion From this model various properties are derived such as the temperature dependence of the magnetic moment and the susceptibility By including magneto - volume effects an application to Invar alloys is shown Finally the properties of the spin fluctuations are derived from a Landau - Ginzburg model A discussion of the Curie temperature in itinerant electron ferromagnets is given

Defect and fluctuation effects at the incommensurate-commensurate phase transition in Rb2ZnCl4

Abstract: The influence of defects and thermal fluctuations on the incommensurate-commensurate transition in modulated ferroelectric structures is studied. It is shown that the deviations near Tc from the equilibrium Landau theory can be understood in terms of an intermediate defect-dominated phase which they describe with a model of random internal fields. Choosing Rb2ZnCl4 as an example for quantitative comparison the authors use NMR, dielectric and X-ray satellite broadening data to evaluate the internal fields, the variation of the soliton density and the defect pinning energies. The roughness of the discommensuration walls in Rb2ZnCl4 is also estimated.

Landau theory of the Mott transition in the fully frustrated Hubbard model in infinite dimensions

Abstract: We discuss the solution of the Mott transition problem in a fully frustrated lattice with a semicircular density of states in the limit of infinite dimensions from the point of view of a Landau free energy functional. This approach provides a simple relation between the free energy of the lattice model and that of its local description in terms of an impurity model. The character of the Mott transition in infinite dimensions, (as reviewed by Georges, Kotliar, Krauth and Rozenberg, Rev. Mod. Phys. 68, 13 (1996)) follows simply from the form of the free energy functional and the physics of quantum impurity models. At zero temperature, below a critical value of the interaction U, a Mott insulator with a finite gap in the one particle spectrum, becomes unstable to the formation of a narrow band near the Fermi energy. Using the insights provided by the Landau approach we answer questions raised about the dynamical mean field solution of the Mott transition problem, and comment on its applicability to three dimensional transition metal oxides.

Crystallography and structural phase transitions, an introduction

Abstract: Structural phase transitions which involve the generation of lattice strain (i.e. in ferroelastic and co-elastic crystals) are reviewed. Landau–Ginzburg theory is found to lead to an appropriate description of order parameters following the theoretical predictions over large temperature intervals. A quantum extension of Landau–Ginzburg theory is presented which describes the saturation of order parameters at low temperatures. Coupling between different order parameters is relevant if more than one phase transition (or lattice instability) occurs in a crystal. Finally, the importance of microstructures and kinetic processes for the structural behaviour of crystals is pointed out.