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Showing papers on "Landau theory published in 2000"


Journal ArticleDOI
TL;DR: In the higher Landau level (nu = 5/2), a first-order phase transition separating a compressible striped phase from a paired quantum Hall state, which is identified as the Moore-Read state.
Abstract: We consider the two lowest Landau levels at half filling. In the higher Landau level $(\ensuremath{ u}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5/2)$, we find a first-order phase transition separating a compressible striped phase from a paired quantum Hall state, which is identified as the Moore-Read state. The critical point is very near the Coulomb potential and the transition can be driven by increasing the width of the electron layer. We find a much weaker transition (either second-order or a crossover) from pairing to the composite fermion Fermi-liquid behavior. A very similar picture is obtained for the lowest Landau level, but the transition point is not near the Coulomb potential.

241 citations


Journal ArticleDOI
TL;DR: In the context of the dynamical mean-field theory of the Hubbard model, an order parameter for the finite temperature Mott end point is identified and a Landau functional of the order parameter is derived.
Abstract: In the context of the dynamical mean-field theory of the Hubbard model, we identify microscopically an order parameter for the finite temperature Mott end point. We derive a Landau functional of the order parameter. We then use the order parameter theory to elucidate the singular behavior of various physical quantities which are experimentally accessible.

147 citations


Journal ArticleDOI
TL;DR: In this article, the surface nucleation of superconductivity and the value of the upper critical field HC3 for superconductors occupying arbitrary bounded smooth domains in R3 were studied.

103 citations


Journal ArticleDOI
TL;DR: A review of collective phenomena in atomic and quasi-atomic systems is presented in this paper, where the fundamental unity of the subject is stressed by appealing to a simple conceptual scheme, namely the Landau theory of wave propagation applied to a Fermi fluid.
Abstract: A review of collective phenomena in atomic and quasi-atomic systems is presented. The fundamental unity of the subject is stressed by appealing to a simple conceptual scheme, namely the Landau theory of wave propagation applied to a Fermi fluid. Collective giant resonances in nuclei, atoms, metallic clusters and fullerenes are all discussed and related to each other. Single-photon dipole, two-photon and quadrupole excitation are considered, as well as the observation of harmonics, and the enhancement of double excitations by a giant resonance. Other near-threshold phenomena are discussed, and experiments involving strong-field lasers are also considered in this context.

64 citations



Journal ArticleDOI
TL;DR: The structure of LaAlO3 has been investigated around the phase transition at T(c) ≃ 800 K by neutron powder diffraction in vacuum and by X-ray powder diffusion under nitrogen atmosphere as well as by a very high resolution synchrotron experiment in air as mentioned in this paper.
Abstract: The structure of LaAlO3 has been investigated around the phase transition at T(c) ≃ 800 K by neutron powder diffraction in vacuum and by X-ray powder diffraction under nitrogen atmosphere as well as by a very high resolution synchrotron experiment in air. The results were analysed in frame of the Landau theory using the fluctuation-dissipation theorem to relate the susceptibility to the atomic displacement parameters. The room temperature structure is a rhombohedrally distorted perovskite structure, space group R3c, which undergoes a transition to the ideal perovskite structure, space group Pm3m, at high temperatures. The order parameter is a rotation of the O6-octahedron described by one χ(O)-parameter. This parameter and the spontaneous strain (c/a - √6), as well as the relevant atomic displacement parameter U(op) 11(O) in the order parameter system, show a critical behaviour in agreement with a second order phase transition. Although the critical exponents of the order parameter and strain show the expected coupling behaviour, there is a striking difference of the transition temperature: the metric becomes cubic roughly 30 K below the proper T(c). This is related to spontaneous formation of domains imposing the average cubic symmetry via internal stresses.

42 citations


Journal ArticleDOI
TL;DR: In this paper, the behavior of a thin lubrication layer is described in a model combining the Landau theory of phase transformations and the Frenkel-Kontorova model, and the kinetic equation for the shear modulus is obtained and solved together with the equation of overdamped motion of the layer.

41 citations


Journal ArticleDOI
TL;DR: In this paper, a Landau-Ginzburg functional of two order parameters (charge-density φ and mass-density deviation η) is developed in order to yield a field theory relevant to ionic lattice gases as well as a family of off-lattice models of ionic fluids that go beyond the restricted primitive model (RPM).

36 citations


Journal ArticleDOI
TL;DR: In this paper, a generalized hydrodynamic theory is derived in the long-wave limit of a kinetic equation, which does not rest on the requirement of a local equilibrium, and it is shown that nonequilibrium effects qualitatively change the collective dynamics in comparison with the predictions of the heuristic Bloch's hydrodynamics.
Abstract: Generalized hydrodynamic theory, which does not rest on the requirement of a local equilibrium, is derived in the long-wave limit of a kinetic equation. The theory bridges the whole frequency range between the quasistatic (Navier-Stokes) hydrodynamics and the high-frequency (Vlasov) collisionless limit. In addition to pressure and velocity the theory includes new macroscopic tensor variables. In a linear approximation these variables describe an effective shear stress of a liquid and the generalized hydrodynamics recovers the Maxwellian theory of highly viscous fluids---the media behaving as solids on a short time scale, but as viscous fluids on long-time intervals. It is shown that the generalized hydrodynamics can be applied to the Landau theory of Fermi liquid. Illustrative results for collective modes in confined systems are given, which show that nonequilibrium effects qualitatively change the collective dynamics in comparison with the predictions of the heuristic Bloch's hydrodynamics. Earlier improvements of the Bloch theory are critically reconsidered.

35 citations


Journal ArticleDOI
TL;DR: In this article, the authors considered a model superlattice consisting of two coupling ferroelectric materials within the framework of Landau phenomenological theory and studied the effects of the coupling between two sublattices on the polarizations.

34 citations


Journal ArticleDOI
TL;DR: The important physical effect is that the effective field of neighboring spins is influenced by the spin state of the central spin, which leads to estimates of T(c) more accurate than those obtained from the Bethe-Peierls-Weiss approximation.
Abstract: The critical temperature T(c) of Ising models is obtained quite accurately by simple improvements over the standard molecular-field theory. The important physical effect we include is that the effective field of neighboring spins is influenced by the spin state of the central spin. When used in combination with a self-consistency condition, this correlated molecular-field theory leads to estimates of T(c) more accurate than those obtained from the Bethe-Peierls-Weiss approximation.


Journal ArticleDOI
TL;DR: In this paper, the primary and secondary order parameters for the three ferroelastic martensitic transformations that occur in the Au-Cd binary, and in the Ti-Ni-M (M = Fe, At, Cu) pseudo-binary shape-memory alloys are identified.
Abstract: On the basis of group theoretical symmetry criteria, the primary and secondary order parameters (OP's) have been identified for the three ferroelastic martensitic transformations that occur in the Au-Cd binary, and in the Ti-Ni-M (M = Fe, At, Cu) pseudo-binary shape-memory alloys, viz (i) from the cubic β 2 austenite parent phase (B2 structure) to the rhombohedral (R) ζ' 2 product phase of P3 symmetry, (ii) from the β 2 to the orthorhombic (γ 2 ) product phase of Pmma symmetry (B19 structure), and (iii) from the B19 to the monoclinic B19'structure of P2 1 /m symmetry. For all three transformations, the Landau free energy and the relations between the primary OP and the atom shuffle displacements are given for the transition to a single product phase variant. For case (i), the 12 experimentally measured structural (shuffle) parameters of the R phase can be accounted for and fitted by only two theoretical model parameters, giving satisfactory agreement with the (only available) room temperature data for Au .505 Cd .495 ; for Ti .4977 Ni .5023 larger discrepancies, but mostly within the relatively large experimental error are found. For the two cases (ii) and (iii), the two shuffle displacements each can be fitted exactly by the two theoretical model parameters required.

Journal ArticleDOI
TL;DR: In this article, experimental data for the Pm 3 m − I 4 mcm phase transitions in the perovskite crystals KMn1− x Ca x F3 and SrTiO3 were presented.
Abstract: We present experimental data for the Pm 3 m – I 4/ mcm phase transitions in the perovskite crystals KMn1− x Ca x F3 and SrTiO3. Comparison of calorimetric data (latent heat and specific heat) with order parameter data (measured with X-ray rocking methods) indicates that these transitions follow mean-field behaviour, and may be described using Landau potentials where the free energy expansion includes terms up to Q 6. This potential is characteristic of transitions close to the tricritical point. Comparison of the behaviour of SrTiO3 and KMnF3 indicates that KMnF3 is closer to the tricritical point; a small amount of substitution of Ca for Mn causes the transition to cross the tricritical point from first order to second order behaviour.

Journal ArticleDOI
TL;DR: In this article, the authors extend the time-dependent effective theory for the Goldstone field (the phase of the pair field) with s-wave interactions to finite temperature and show that when Landau damping is neglected, the effective theory can be written as a local timedependent non-linear Schrodinger Lagrangian (TDNLSL) which preserves the Galilean invariance of the zero temperature effective theory and is identified with the superfluid component.
Abstract: We extend to finite temperature the time-dependent effective theory for the Goldstone field (the phase of the pair field) $ \theta $ which is appropriate for a superfluid containing one species of fermions with s-wave interactions, described by the BCS Lagrangian. We show that, when Landau damping is neglected, the effective theory can be written as a local time-dependent non-linear Schrodinger Lagrangian (TDNLSL) which preserves the Galilean invariance of the zero temperature effective theory and is identified with the superfluid component. We then calculate the relevant Landau terms which are non-local and which destroy the Galilean invariance. We show that the retarded $\theta$-propagator (in momentum space) can be well represented by two poles in the lower-half frequency plane, describing damping with a predicted temperature, frequency and momentum dependence. It is argued that the real parts of the Landau terms can be approximately interpreted as contributing to the normal fluid component.

Journal ArticleDOI
TL;DR: In this article, the authors studied ground-state properties and phonon dispersion curves of a classical linear-chain model describing a crystal with an incommensurate phase with an extra fourth-order term added to it.
Abstract: Ground-state properties and phonon dispersion curves of a classical linear-chain model describing a crystal with an incommensurate phase are studied. This model is the DIFFOUR (discrete frustrated ${\ensuremath{\varphi}}^{4})$ model with an extra fourth-order term added to it. The incommensurability in these models may arise if there is frustration between nearest-neighbor and next-nearest-neighbor interactions. We discuss the effect of the additional term on the phonon branches and phase diagram of the DIFFOUR model. We find some features not present in the DIFFOUR model such as the renormalization of the nearest-neighbor coupling. Furthermore, the ratio between the slopes of the soft phonon mode in the ferroelectric and paraelectric phase can take on values different from $\ensuremath{-}2.$ Temperature dependences of the parameters in the model are different above and below the paraelectric transition, in contrast with the assumptions made in Landau theory. In the continuum limit this model reduces to the Landau free-energy expansion for type-II incommensurate crystals and it can be seen as the lowest-order generalization of the simplest Lifshitz-point model. Part of the numerical calculations have been done by an adaption of the effective potential method, originally used for models with nearest-neighbor interaction, to models with also next-nearest-neighbor interactions.

Journal ArticleDOI
TL;DR: In this article, the results of magnetic measurements in MnAs prepared by ball-milling and single crystalline ferromagnetic Ni 2 MnGa specimens exhibiting magnetostructural and martensitic transformations respectively are presented.
Abstract: The results of magnetic measurements in MnAs prepared by ball-milling and single crystalline ferromagnetic Ni 2 MnGa specimens exhibiting magnetostructural and martensitic transformations respectively are presented. Some details of the transformation behaviour and giant magnetoelastic response of these compounds are explained within the Bean-Rodbell model and Landau approach.


Journal ArticleDOI
TL;DR: In this paper, the rotator-II-to-rotator-I phase transition in alkanes is studied within Landau theory and the effect of pressure on the transition is also examined.
Abstract: The rotator-II to rotator-I phase transition in alkanes is studied within Landau theory. The effect of pressure on the transition is also examined. The transition is found to be first order, even at elevated pressure, with the transition temperature increasing with pressure. The various thermodynamic quantities are calculated near the transition. The Landau coefficients are calculated for various chain lengths from experimental data. The values of the coefficients are decreasing with increasing chain length.

Journal ArticleDOI
TL;DR: In this article, the influence of the external magnetic field on the martensitic transformation from cubic parent phase (P) to five-layered martensite (5M-martensite) is analyzed.
Abstract: The influence of hydrostatic pressure, uniaxial stress and magnetic field on the martensitic transformation temperatures for the ferromagnetic single crystalline Ni-Mn-Ga alloys is studied. It is shown that the experimental results are satisfactorily described by the Landau theory. Ni-Mn-Ga L2 1 -type ordered alloys exhibit a number of the first order and weak first order structural transformations in a ferromagnetic or paramagnetic parent phase depending on the alloy composition and being either thermally or stress activated [1,2]. Most of these phase transformations are of the martensitic type, i.e., they are accompanied by the spontaneous elastic strains forming a multicomponent order parameter in the Landau expansion for the Gibbs potential (see [3] and references therein). In this work we analyze the influence of the external fields (mechanical and magnetic) on the martensitic transformation (MT) from cubic parent phase (P) to five-layered martensitic one (5M-martensite) usually exhibited by the ferromagnetic ordered Ni-Mn-Ga alloys. In accordance with [4], we treat the 5M-martensite as a twinned tetragonal phase and, so, describe the experimental results in the framework of the theory of cubic-tetragonal MT [5]. The original experimental data of high magnetic field influence on MT in near stoichiometric Ni 2 MnGa compound are presented to compare with the theoretical estimations.

Journal ArticleDOI
TL;DR: In this article, the influence of radiation defects on the phase transition in ferroelectric crystals was studied by calorimetric experiments and the specific heats of TGSe and DTGSe were measured.

Journal ArticleDOI
TL;DR: A simplified model of the Ginzburg Landau model of superconductivity is derived in the asymptotic limit of very small thickness and it is shown that under certain conditions there is no nucleation ofsuperconductivity at all.

Journal ArticleDOI
Xiaomei Lu1, Jinsong Zhu1, Zhiguo Liu1, Xiaoshan Xu1, Yening Wang1 
TL;DR: In this paper, an uneven distribution of stress in the thickness direction was introduced into Landau theory to investigate the critical behavior of phase transition of ferroelectric thin films, and the Curie temperature T C was calculated to increase and decrease for compressive and tensile stress cases, respectively.

Journal ArticleDOI
TL;DR: The Lifshitz point in the (H,T) phase diagram of a ferroelectric liquid crystal in a transverse magnetic field has been determined using photon correlation spectroscopy and linear electrooptic response measurements.
Abstract: The Lifshitz point in the (H,T) phase diagram of a ferroelectric liquid crystal in a transverse magnetic field has been determined using photon correlation spectroscopy and linear electrooptic response measurements. The extrapolated Lifshitz magnetic field is 25(1+/-0.1) T for a smectic-C* material with an unperturbed helical period of approximately 6 mm, and the Lifshitz point is located approximately 100 mK above the zero-field transition temperature. We have observed the reentrant helical modulated smectic-C* phase just below the lambda line. The width of this phase is 100 mK at the low temperature critical field H(c) and decreases continuously to zero as we approach the Lifshitz point. The phase boundary between the reentrant phase and the smectic-A phase is of second order, whereas the phase boundary with the unwound smectic-C(*) phase is of first order far away from the Lifshitz point and becomes of second order close to the Lifshitz point. The order parameter dynamics is discussed within the Landau theory.

Journal ArticleDOI
TL;DR: In this article, a non-Markovian Levinson-type kinetic equation is derived from the theory of dense gases, and the derived non-local kinetic equation unifies the Landau theory of quasiparticle transport with the classical kinetic theory of densities.
Abstract: The finite duration of the collisions in Fermionic systems as expressed by the retardation time in non-Markovian Levinson-type kinetic equations is discussed in the quasiclassical limit. We separate individual contributions included in the memory effect resulting in (i) off-shell tails of the Wigner distribution, (ii) renormalization of scattering rates and (iii) of the single-particle energy, (iv) collision delay and (v) related non-local corrections to the scattering integral. In this way we transform the Levinson equation into the Landau-Silin equation extended by the non-local corrections known from the theory of dense gases. The derived nonlocal kinetic equation unifies the Landau theory of quasiparticle transport with the classical kinetic theory of dense gases. The space-time symmetry is discussed versus particle-hole symmetry and a solution is proposed which transforms these two exclusive pictures into each other.

Journal ArticleDOI
TL;DR: In this article, a corresponding Landau theory of phase transitions is formulated for half-doped manganites and a unified picture for the scenario of the phase transitions and their nature with respect to the variation of the tolerance factor of the manganite is provided.
Abstract: The order parameters of the magnetic, charge, and structural orders at half-doped manganites are identified. A corresponding Landau theory of the phase transitions is formulated. Many structural and thermodynamical behaviors are accounted for and clarified within the framework. In particular, the theory provides a unified picture for the scenario of the phase transitions and their nature with respect to the variation of the tolerance factor of the manganites. It also accounts for the origin of the incommensurate nature of the orbital order and its subsequently accompanying antiferromagnetic order.


Journal ArticleDOI
TL;DR: In this paper, the authors study the Ginzburg-Landau equations and find that within a particular range of parameters, the presence of uniformly propagating localized objects behaving as coherent structures.

Journal ArticleDOI
TL;DR: In this article, the stability of bifurcating solutions for the Ginzburg-Landau equations was studied for a superconductor with a film of thickness 2d submitted to an external magnetic field.
Abstract: We consider the bifurcating solutions for the Ginzburg–Landau equations when the superconductor is a film of thickness 2d submitted to an external magnetic field. We refine some results obtained earlier [1] on the stability of bifurcating solutions starting from normal solutions. We prove, in particular, the existence of curves d [map ] κ0(d), defined for large d and tending to 2−1/2 when d [map ] +∞ and κ [map ] d1(κ), defined for small κ and tending to √5/2 when κ [map ] 0, which separate the sets of pairs (κ, d) corresponding to different behaviour of the symmetric bifurcating solutions. In this way, we give in particular a complete answer to the question of stability of symmetric bifurcating solutions in the asymptotics ‘κ fixed-d large’ or ‘d fixed-κ small’.

Journal ArticleDOI
TL;DR: The d-dimensional complex Ginzburg-Landau (GL) model is solved according to a variational method by separating phase and amplitude by showing that the validity of the approach lies precisely in the first-order domain.
Abstract: The d-dimensional complex Ginzburg-Landau (GL) model is solved according to a variational method by separating phase and amplitude. The GL transition becomes first order for high superfluid density because of phase fluctuations. We discuss its origin with various arguments showing that, in particular for d = 3, the validity of our approach lies precisely in the first-order domain.