Landau theory

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

Lattice dynamics representation theory versus isotropy subgroup method with application to M5 mode instability in CsCl structure

Abstract: The Landau theory for ferroic phase transitions occurring in materials with CsCl structure (space group O1 h, Pmm) induced by M− 5 mode softening is developed by two different procedures: (i) The physically transparent lattice dynamical approach in conjunction with standard group representation theory, and (ii) the abstract, powerful group theoretical approach employing the concepts of isotropy subgroups and subduction frequencies. These two methods are outlined and their respective merits compared. The Landau free energy is given up to sixth order in the six-component primary order parameter. All 26 symmetry allowed product phases are identified and described in terms of their atomic displacements. Specifically, an improper ferroelastic transition to a tetragonally distorted low symmetry phase (D1 4, 14/mmm) and its atomic displacements observed in x-ray and neutron scattering experiments on LaAg1-x Inx (x ∼ 0.2) are confirmed. For this transition another symmetry allowed secondary order paramet...

Chiral-racemic phase diagram of a blue-phase liquid crystal

Abstract: We have measured the phase diagram for mixtures of chiral and racemic cholesteric S-(+)-4-(2-methylbutyl)phenyl-4-decyloxyben- zoate (CE6) in order to study the effect of changing chirality on the appearance of the cholesteric blue phases. We have also measured the latent heats at the isotropic transitions. Our phase diagram is compared with the Landau theory of Hornreich and Shtrikman and the data of Marcus and Goodby.

Yet another criticality of water

Abstract: A phase behavior around the transition between ice VII and a plastic phase of water is investigated by molecular dynamics simulation and the subsequent analysis on the basis of Landau theory. The prior works have predicted that the phase transition between ice VII and plastic ice is a first-order transition on the ground of a weak hysteresis and so on. A rigorous survey in the present report, however, augments their prediction with new evidence that a first-order phase transition line gives way to a second-order one at higher pressures, where a tricritical point joins these phase boundaries together. Critical phenomena are also observed whereby, other than that associated with the hypothetical critical point in the deeply supercooled state, which could influence the physical properties in a wide range of temperatures and pressures. A new critical behavior is affirmed by the result that the scaling law holds at any pressure on the second-order phase transition line for which the critical exponents are estimated. We introduce an appropriate order parameter to obtain the Landau free energy functional and the change in the functional against temperature accounts for the phase behaviors. This also enables an estimate of the coexistence and the spinodal lines at pressures below the tricritical point, all of which compensate those obtained directly by molecular dynamics simulations. These results allow us to anticipate that the critical fluctuations may give us a clue for determining the phase boundary experimentally.

A Ginzburg-Landau Theory For Ni-Mn-Ga

Abstract: We present an effective Ginzburg-Landau theory for ferromagnetic cubic Ni-Mn-Ga in which structural and magnetic phase transitions take place. The general problem of a cubic ferromagnet is taken into account by fitting the parameters of the Ginzburg-Landau functional to experimental data. This enables us to obtain a realistic phase diagram for Ni-Mn-Ga.