Showing papers on "Landau theory published in 1975"
TL;DR: In this article, a Landau theory is proposed for charge-density waves (CDW) in transition-metal dichalcogenides with the charge density as an order parameter, which predicts the sequence of phases, normal-state, commensurate-CDW, with decreasing temperature, separated by first-order phase transitions.
Abstract: A Landau theory is proposed for charge-density waves (CDW) in transition-metal dichalcogenides with the charge density as an order parameter. The theory predicts the sequence of phases, normal-state---incommensurate-CDW---commensurate-CDW with decreasing temperature, separated by first-order phase transitions. The peaks in charge density lie at "lattice sites" of a hexagonal crystal and for the incommensurate case the theory predicts phononlike distortions of the CDW "lattice" as well as dislocations. Impurities pin the charge density wave, broaden the phase transitions, and stabilize the incommensurate state relative to the commensurate state.
335 citations
TL;DR: A lattice-gas model of ternary fluid mixtures is presented, and mean-field theory indicates the existence of a fourth-order critical point in the spin-1 model of Blume, Emery, and Griffiths.
Abstract: We present a lattice-gas model of ternary fluid mixtures. Within the mean-field approximation, we study a nonsymmetric tricritical point in this model. We compare our results to the experimental observations on the system ethanol-water-carbon-dioxide. In the course of our work, we have studied a Landau theory describing the neighborhood of a fourth-order critical point. Also, we have noted that mean-field theory indicates the existence of a fourth-order critical point in the spin-1 model of Blume, Emery, and Griffiths, corresponding to $Kl0$, $J+Kg0$.
97 citations
55 citations
46 citations
TL;DR: In this paper, a dynamical Landau theory is proposed to describe the coupled motion of phonons and charge-density waves near the CDW instability in transition-metal dichalcogenides.
Abstract: A dynamical Landau theory is proposed to describe the coupled motion of phonons and charge-density waves (CDW) near the CDW instability in transition-metal dichalcogenides. The dynamic structure factor is shown to exhibit a Kohn anomaly and a diverging central mode.
38 citations
TL;DR: In this article, the authors measured the thermal strain along the X-axis of crystalline quartz in the vicinity of the αβ transition and showed that the onset of long range order, which previously had been thought to reflect non-classical behavior, can be adequately described by classical Landau theory.
36 citations
TL;DR: Using the Landau theory of phase transitions, Arrott plots, the high field and the paramagnetic susceptibility and the magnetization of heterogeneous weakly ferromagnetic alloys are calculated analytically for a simple model for the heterogeneity as discussed by the authors.
30 citations
TL;DR: In this paper, the generalized Landau theory of phase transitions is extended to cover the ferromagnetic regime where the Landau coefficient B has to be included, and the theory is applied to dilute Pd-Ni 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.
26 citations
TL;DR: In this article, the authors investigated how the Landau theory may break down at first-order transition (FOT) due to the fact that the transition temperature Tc is located near two critical points: the metastable critical point (MCP), which is the stability limit of the ordered phase, and the fluid-like critical point, at which the conjugate H of the order parameter is not null.
Abstract: The author investigates how the Landau theory may break down at a first-order transition (FOT). This may happen because the transition temperature Tc is located near two critical points: the metastable critical point (MCP), which is the stability limit of the ordered phase, and the fluid-like critical point (FLCP), at which the conjugate H of the order parameter is not null. Using the Ginzburg criterion, it is found that one inequality expresses the condition that Tc be outside the two critical regions. The results are applied to two types of FOT: one located near a tricritical point and the other located near an isolated critical point. When Tc is inside a critical region, it is found that the critical indices of the MCP are beta 1= beta (critical index of the FLCP) and alpha 1= gamma 1=1- beta . The critical region (0.2 degrees C) of BaTiO3 near the FLCP is determined and the experimental results of SbSI and KMnF are discussed.
11 citations
TL;DR: In this paper, the authors used optical birefringence measurements to determine the order-disorder phase transition in the mixed system NH4Cl1-xBrx.
Abstract: Around the order-disorder phase transition in the mixed system NH4Cl1-xBrx the course of the order parameters has been determined using optical birefringence measurements have been discussed on the basis of the Landau theory. The smearing of the transition temperature from strains and inhomogeneities in concentration and sample temperature was taken into account. The result is that the beta , gamma transition in the whole mixed system is of first-order nature. The relative size of the discontinuity in birefringence, Delta n(To)/ Delta n(120), is clearly x-dependent, varying from about 0.3(x=0.12) to 0.06 (x=0.43), rising again to 0.14 for NH4Br. Around middle concentrations, the system is close to a tricritical point.
10 citations
TL;DR: In this article, it was shown that a theory with an order parameter of one real component, phi, with u3 phi 3 local interaction exhibits a first order phase transition for mod u3 mod >u3c>0, a critical point at u3 = u3c, and no transition for the mod u 3 mod 0, in contradiction to the Landau theory which predicts a first-order transition for all u3>0.
Abstract: The authors show that a theory with an order parameter of one real component, phi , with u3 phi 3 local interaction exhibits-due to fluctuations-a first order phase transition for mod u3 mod >u3c>0, a critical point at u3=u3c, and no transition for mod u3 mod 0. This is in contradiction to the Landau theory which predicts a first order transition for all u3>0. The relation of this failure of Landau's theory to questions of symmetry breaking is discussed.
TL;DR: In this paper, a linear optical birefringence was used to detect the first order transition of NH4Br in the critical region T > 0.9T0 by the Landau theory and a simple power law.
TL;DR: Using a Ginzburg-Landau functional description of the laser, an expression for the photon current density, analogous to that for the electronic current in superconductors, was obtained in this paper.
TL;DR: In this paper, the authors examined the martensitic transformation in A15 compounds in the presence of internal strains and of external mechanical stress on the basis of the Landau theory of phase transitions.
Abstract: The martensitic transformation in A15 compounds in the presence of internal strains and of external mechanical stress is examined on the basis of the Landau theory of phase transitions. The free energy of the model coincides with the free energies of the three-state Potts model and provides an explanation for the different martensitic transition temperatures for Nb3Sn and V3Si crystals. It is argued that in these compounds the linear chains of Nb and V atoms may be broken in the tetragonal phase. The critical behaviour is discussed.
01 Jan 1975
TL;DR: In this paper, the authors present optical heterodyne measurements of the Taylor instability in a rotating fluid which confirm that such a potential does in fact correctly describe the dynamics of the fluid near the critical point (although outside the region where fluctuations are important).
Abstract: According to Graham 1, the behavior of a fluid near a hydrodynamic instability should be determined by a generalized potential Ф which is of the same form as the Gibbs potential in the Landau theory of phase transitions. This potential is predicted to describe the dynamics of a suitably defined order parameter both above and below the critical point. In this paper we present optical heterodyne measurements of the Taylor instability in a rotating fluid which confirm that such a potential does in fact correctly describe the dynamics of the fluid near the critical point (although outside the region where fluctuations are important). In particular, we have observed a divergence of the response time associated with the flatness of the potential near the critical point.
01 Dec 1975
TL;DR: The spin and spin-isospin symmetry energies of nuclear matter and the spin and isospin dependent terms of the nuclear single-particle potential at the Fermi surface are calculated within the frame of the Landau theory of the normal FermI liquid from the existing sets of Landau parameters as mentioned in this paper.
Abstract: The spin and spin-isospin symmetry energies of nuclear matter and the spin and isospin dependent terms of the nuclear single-particle potential at the Fermi surface are calculated within the frame of the Landau theory of the normal Fermi liquid from the existing sets of the Landau parameters. The possibility of the relation of these parameters to the experimental energies of certain collective nuclear excited states is pointed out. The results are also applied to the calculation of the symmetry and the spin-spin terms in the low energy nuclear optical model potential.
Journal Article•
TL;DR: In this paper, a microscopic theory of the electromagnetic radiation emitted by a highly excited nucleus is developed on the basis of the Landau theory of a Fermi liquid, and closed formulae are obtained for the mean radiative width and its mean square fluctuation from level to level.
Abstract: A microscopic theory of the electromagnetic radiation emitted by a highly excited nucleus is developed on the basis of the Landau theory of a Fermi liquid. Closed formulae are obtained for the mean radiative width and its mean square fluctuation from level to level. The temperatures of many nuclei are found from the observed widths. The relaxation time is estimated from the experimental data on the radiativewidth fluctuations. The regions of applicability of the various types of relations between the relaxation time and the lifetime of the compound nucleus, as well as the relevant physical consequences, are discussed.
TL;DR: In this paper, the grand canonical partition function written as a Feynman path integral over the order parameter is calculated numerically within the framework of a Ginzburg-Landau theory for a one dimensional van der Waals system.
Abstract: The grand canonical partition function written as a Feynman path integral over the order parameter is calculated numerically within the framework of a Ginzburg-Landau theory for a one dimensional van der Waals system. The equation of state is calculated. The results show that the transition is of quasi first order.