Showing papers on "Landau theory published in 1974"
TL;DR: In this paper, Anderson's statement that in the low-temperature limit the usual Kondos-d model evolves toward a fixed point in which the effective exchange coupling of the impurity with the conduction electrons is infinitely strong is taken as granted.
Abstract: We take as granted Anderson's statement that in the low-temperature limit the usual Kondos-d model evolves toward a fixed point in which the effective exchange coupling of the impurity with the conduction electrons is infinitely strong. The low-temperature properties (T«T
K) are then described phenomenologically in the same spirit as the usual Landau theory of Fermi liquids. The specific heat, spin susceptibility, and resistivity are expressed in terms of a small number of numerical parameters. In the strong coupling case the latter may be obtained via perturbation theory; in the opposite weak coupling limit they must be fitted to Wilson's recent numerical results.
703 citations
TL;DR: In this article, the authors describe the work that has already been done, and also mention work that is in progress, but is not as yet properly understood, in β-Tungsten research.
Abstract: Publisher Summary This chapter describes the work that has already been done, and also mentions work that is in progress, but is not as yet properly understood, in β-Tungsten research. Regarding work that has already been done, it is seen that elastic anomalies and martensitic phase transformations appear to be quite a general phenomenon; they require a large deformation potential, a large electronic density of states at the Fermi level (that may result from Van Hove singularities), and a degeneracy of the electronic states (with the same value of k, or with different ones). To a certain extent, they can be described by the Landau theory of order-disorder transformation, but most commonly they may be expected to be first-order transitions. The various microscopic models proposed so far to account for these anomalies; all predict a Landau type behavior. Therefore, this behavior is not a test for the applicability of one or another of these models. Lattice instabilities due to optical phonons should also be present, but they have not been observed so far in the β-tungstens, except for Nb3Sn, probably because they have not been looked for (except in V3Si, where they are not present). They may be associated with sharp peaks in the ultrasonic attenuation as a function of temperature, such as those observed in V3Ge.
102 citations
TL;DR: In this paper, a model for granular superconductors consisting of an array of small superconducting particles interacting by Josephson coupling through insulating barriers is considered and the conditions for observing the phase-locking transition distinct from quasiordering within the grains are found.
Abstract: We consider a model for granular superconductors consisting of an array of small superconducting particles interacting by Josephson coupling through insulating barriers. We obtain systematically the various critical regions, critical temperature shifts, and crossover regions between zero- and three-dimensional behavior as functions of measurable sample parameters. The qualitative behavior of the system in the various regimes is analyzed and results for the specific heat and fluctuation conductivity in the Gaussian region above ${T}_{c}$ are obtained. The possibility of obtaining large critical regions is emphasized. The conditions for observing the phase-locking transition distinct from quasiordering within the grains are found. Theoretical predictions are compared with existing experimental results.
91 citations
TL;DR: In this article, a time-dependent Landau theory is proposed for the smectic-$A$-nematic phase transition and it is shown that the nematic viscosity coefficients exhibit a pretransition effect similar to that for the elastic constants.
Abstract: A time-dependent Landau theory is proposed for the smectic-$A$-nematic phase transition. It is shown that the nematic viscosity coefficients exhibit a pretransition effect similar to that for the elastic constants.
54 citations
TL;DR: In this article, it was shown that fluctuations of intermediate wavelengths are the crucial effect producing non-classical exponent (intermediate wavelengths are much larger than the range of forces, much smaller than the correlation length).
48 citations
TL;DR: In this paper, the authors show that if the unperturbed propagator of fluctuations is expressed in terms of the full susceptibility (mass renormalization) then the width of the critical region follows systematically.
Abstract: Following a critique of the various arguments leading to Ginzburg's criterion for the width of the critical region the author shows that if the unperturbed propagator of fluctuations is expressed in terms of the full susceptibility (mass renormalization) then the width of the critical region follows systematically. The procedure gives, automatically, the width of the region about the real transition temperature for which both the Landau and the Ginzburg-Landau theories are valid. Exactly the same logic applies above and below the transition temperature.
39 citations
TL;DR: In this article, the authors investigated the onset of three-dimensional ordering as a function of the interchain coupling and the order-parameter correlation function aboveTc and compared the results with neutron scattering experiments on the quasi-linear conductor K2Pt(CN)4Br 0.3 · 3 D2O.
Abstract: Fluctuations in a system of weakly coupled linear chains are investigated within the functional generalization of the Landau theory. The onset of three-dimensional ordering as a function of the interchain coupling and the order-parameter correlation function aboveTc are discussed. The results are compared with neutron scattering experiments on the quasi-linear conductor K2Pt(CN)4Br0.3 · 3 D2O.
35 citations
28 citations
TL;DR: In this article, the second order gradient terms in the free energy expansion of an anisotropic BCS-superfluid were calculated in weak coupling theory and the supercurrents and dispersion law of orbital waves were calculated for the Anderson-Brinkman state.
17 citations
TL;DR: In this article, the free energy per component of an isotropic one-dimensional Ginzburg-Landau field with n components was calculated to order n-2 by evaluating the appropriate Feynman graphs.
Abstract: The free energy per component of an isotropic one-dimensional Ginzburg-Landau field with n components is calculated to order n-2 by evaluating the appropriate Feynman graphs. The result agrees with that of Ferrell and Scalapino (1974) obtained by solving the equivalent anharmonic oscillator problem, but the method has greater generality.
14 citations
01 Jan 1974
TL;DR: In this paper, anharmonic lattice dynamical treatment of these effects is used to show that within the framework of a Landau theory quasi-elastic scattering is expected both above and below Tc at some phase transitions, while at others only below T c. The importance of these critical fluctuations may be assessed with the techniques of renormalization group theory.
Abstract: Experimental measurements of light and neutron scattering in materials which undergo displacive structural phase transitions have shown that there is frequently quasi-elastic response in addition to the scattering predicted by the soft mode theory. These measurements are reviewed and the phenomenological theory described. The anharmonic lattice dynamical treatment of these effects is used to show that within the framework of a Landau theory quasi-elastic scattering is expected both above and below Tc at some phase transitions, while at others only below Tc. If critical fluctuations cause a breakdown of the Landau theory close to Tc, then additional quasi-elastic scattering may be expected. The importance of these critical fluctuations may be assessed with the techniques of renormalization group theory.
TL;DR: The diffusion coefficient of liquid 3 He in the collisionless regime, as measured in a porous medium, is temperature independent, in contrast to the T -2 variation in bulk liquid.
TL;DR: In this article, the magnetic phase transition in disordered alloys is discussed on the basis of a phenomenological Landau theory and the critical concentration of disordered Pd-Ni alloys was found to be lower than that obtained previously for a regular lattice.
TL;DR: A lattice dynamical theory is developed for the phase transition in quartz, and the behaviours of various quantities in the vicinity of the transition temperature are discussed in this paper, where it is shown that the order parameter is proportional to the frequency of the soft mode regardless their temperature dependence and the discontinuous change of elastic constants are attributed to this proportionality.
Abstract: A lattice dynamical theory is developed for the phase transition in quartz, and the behaviours of various quantities in the vicinity of the transition temperature are discussed. At temperatures well away from the transition, these behaviours can be interpreted within the framework of the Landau theory. However, drastic deviations from the theory appear in the vicinity of the transition. Therefore an attempt was made to improve the approximation. The present consideration made it possible to interpret qualitatively the behaviours near the transition. It was shown that the order parameter is proportional to the frequency of the soft mode regardless their temperature dependence and the discontinuous change of the elastic constants are attributed to this proportionality. The discontinuous change of the frequency of \(\varGamma_{1}\) mode was predicted by the theory.
TL;DR: In this paper, a free energy functional is proposed for the two-dimensional Ising model below T c which incorporates the correct critical exponents and the anomalous behaviour of the order-parameter correlation function.
TL;DR: The microscopic properties of Invar are discussed in the framework of a generalization of the Landau theory as discussed by the authors, and they are consistent with the R.J. Weiss hypothesis of a first order local transition about 29% of nickel and also the observation of a hysteresis in pulsed field experiments at 77 K.
Abstract: The microscopic properties of Invar are discussed in the framework of a generalization of the Landau theory. They are consistent with the R.J. Weiss hypothesis of a first order local transition about 29% of nickel and also the observation of a hysteresis in pulsed field experiments at 77 K.
01 Jan 1974
TL;DR: In this article, the spin diffusion coefficient of 3He was measured in narrow channels at temperatures low enough for the quasiparticles to be in the collisionless regime and the results were in agreement with modified Landau theory which does not involve the usual temperature-dependent mean free path.
Abstract: The low-temperature properties of bulk liquid 3He are broadly consistent with Landau quasiparticle theory although they do not, in a precise sense, verify its correctness. The temperature dependence in the limit T→0 is that predicted for any Fermi system, and the magnitude of the coefficients cannot be calculated explicitly. Moreover, accurate comparison of the temperature variations below 50 m°K, where it is most significant, is made doubtful by uncertainties in the temperature scale. We report here the results of an experiment of a different sort, namely the direct observation of mean free path effects in the quasiparticles. The present measurements are of the spin diffusion coefficient of 3He confined to narrow channels at temperatures low enough for the quasiparticles to be in the collisionless regime. Our results are in agreement with modified Landau theory which does not involve the usual temperature-dependent mean free path.1 In these experiments the bulk and the mean-free-path-limited diffusion coefficients can be measured virtually coextensively and simultaneously, which greatly facilitates their direct comparison. A similar experiment on heat conduction has already been reported.2
TL;DR: Solutions of the t.d.G.L-equations above the critical current are found for which normal and supercurrents are flowing simultaneously in this paper, where the supercurrent is assumed to be independent of the normal current.