Landau theory

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

Experimental Evidence for a Bragg Glass Density Wave Phase in a Transition-Metal Dichalcogenide

Abstract: Analysis of the spatial dependence of current-voltage characteristics obtained from scanning tunneling microscopy experiments indicates that the charge density wave (CDW) occurring in ${\mathrm{NbSe}}_{2}$ is subject to locally strong pinning by a non-negligible density of defects, but that on the length scales accessible in this experiment the material is in a ``Bragg glass'' phase where dislocations and antidislocations occur in bound pairs and free dislocations are not observed. An analysis based on a Landau theory is presented showing how a strong local modulation may produce only a weak long range effect on the CDW phase.

The structural phase transition in calcium-aluminum compound (CaAl4): a concerted application of Landau theory and energy band theory

Abstract: CaAl[sub 4] undergoes a reversible, structural transformation at 170[degrees]C according to high-temperature X-ray powder diffraction experiments. The high-temperature phase adopts the tetragonal BaAl[sub 4] structure (space group I4/mmm), while the low-temperature phase is monoclinic, C2/m, with lattice parameters, a = 6.1526 (15) [angstrom], b = 6.1730 (13) [angstrom], c = 6.3290 (14) [angstrom], [beta] = 118.026 (16). The Landau theory of phase transitions correctly provided a structural model for the low-temperature phase, which could be subsequently refined. Also, electronic structure calculations on both forms of CaAl[sub 4] allow rationalization of the transformation in terms of changes in local chemical bonding within the Al framework. 26 refs., 8 figs., 8 tabs.

Martensitic phase transition with two-component order parameter in a stressed cubic crystal

Abstract: Martensitic phase transitions in a stressed cubic crystal are studied by means of Landau theory with a two-component order parameter. The stress-temperature phase diagram is analyzed theoretically and is shown to consist of six essentially different regions isolated by the liability lines of austenite, tetragonal martensitic and orthorhombic martensitic phases. The triple point is also present in the phase diagram. The role of the cubic term in the Landau-Ginzburg potential in the description of the phase transition properties is emphasized.

A phenomenological theory of strongly paramagnetic and weakly ferromagnetic dilute alloys

Abstract: An earlier calculation based on the generalized Landau theory of phase transitions is extended to cover the ferromagnetic regime where the Landau coefficient B has to be included. The theory is applied to dilute Pd-Ni alloys. Contrary to the earlier calculation, nearest neighbour pairs of nickel atoms in a matrix consisting of palladium and single nickel impurities are considered. The Landau equation is solved to give the dependence of the magnetization M on external field (Arrott plots) and on the spatial position relative to the impurities. The agreement of the Arrott plots with those observed is good.

Landau theory for a metal-insulator transition.

Abstract: The nonlinear $\sigma$-model for disordered interacting electrons is studied in spatial dimensions $d>4$. The critical behavior at the metal-insulator transition is determined exactly, and found to be that of a standard Landau-Ginzburg-Wilson $\phi^4$-theory with the single-particle density of states as the order parameter. All static exponents have their mean-field values, and the dynamical exponent $z=3$. $\partial n/ \partial \mu$ is critical with an exponent of $1/2$, and the electrical conductivity vanishes with an exponent $s=1$. The transition is qualitatively different from the one found in the same model in a $2+\epsilon$ expansion.