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Landau theory
About: Landau theory is a research topic. Over the lifetime, 2882 publications have been published within this topic receiving 57078 citations.
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TL;DR: The Ginzburg Landau theory for d x 2 - y 2 -wave superconductors is constructed, by starting from the Gor'kov equation with including correction terms up to the next order of ln (T c / T ). Some of the non-local correction terms are found to break the cylindrical symmetry and lead to the fourfold symmetric core structure as discussed by the authors.
Abstract: The Ginzburg Landau theory for d x 2 - y 2 -wave superconductors is constructed, by starting from the Gor'kov equation with including correction terms up to the next order of ln ( T c / T ). Some of the non-local correction terms are found to break the cylindrical symmetry and lead to the fourfold symmetric core structure, reflecting the internal degree of freedom in the pair potential. Using this extended Ginzburg Landau theory, we investigate the fourfold symmetric structure of the pair potential, current and magnetic field around an isolated single vortex, and clarify concretely how the vortex core structure deviates from the cylindrical symmetry in the d x 2 - y 2 -wave superconductors.
13 citations
Abstract: The magnetic field and temperature dependence of the magnetic susceptibility is studied for the ferromagnetic layered manganites SrO(La1−xSrxMnO3)2 in the composition range x=0.32–0.40. In the paramagnetic phase, the susceptibility exhibits an anomalous maximum at an intermediate magnetic field value. The size of this field-induced susceptibility enhancement increases dramatically with x from 10% for x=0.32 to 160% for x=0.40. The temperature dependence of the effect shows a maximum at T≈1.1 TC for all x. Quantitative analysis in terms of the Landau theory of phase transitions enables us to identify a distortion of the free energy F in the paramagnetic phase that is associated with the susceptibility anomaly. This free energy distortion corresponds to a magnetic system that approaches a first order magnetic phase transition as the temperature is lowered toward TC. Such a behavior is indicative of a second, competing order parameter, which is identified as the recently observed charge density wave. In the ...
13 citations
13 citations
TL;DR: In this article, the authors review the description of the orientational ordering transition from an fcc to an sc unit cell which occurs in undoped C60 at a temperature T≈260 K.
Abstract: Various orientation transitions in the fullerenes are described within the Landau theory of phase transitions. Among these we review the description of the orientational ordering transition from an fcc to an sc unit cell which occurs in undoped C60 at a temperature T≈260 K. We also discuss the symmetry of the orientational glass transition which is found via elastic neutron scattering at T≈90 K. We comment on the seemingly spurious transition (so called “2-a transition”) which was claimed to double the size of the unit cell from simple cubic to fcc with eight molecules per unit cell. We also discuss the orientational state of the doped systems M3C60, where M denotes an alkali metal. In this system the C60 molecules are restricted to two “standard” orientations. The resulting Ising model has antiferromagnetic nearest neighbor interactions and nonnegligible four-spin interactions whose properties have recently been discussed. The Landau description of the orientational ordering in C70 is also presented. Here we include a description of the elastic distortion which accompanies orientational ordering.
13 citations
TL;DR: In this article, a simple free energy function consisting of six terms in the polarization components p a and p c reproduces well the phase transition itself and the temperature dependence of spontaneous polarizations.
Abstract: The ferroelectric phase transition in Bi 4 Ti 3 O 12 is interpreted phenomenologically on the basis of a Landau-type free energy. The requirements on the concrete parameter values, necessary to induce the first order tetragonal-monoclinic phase transition in Bi 4 Ti 3 O 12 , are discussed. It turns out that a simple free energy function consisting of six terms in the polarization components p a and p c reproduces well the phase transition itself and the temperature dependence of spontaneous polarizations, while a seventh term is required to reproduce the temperature dependence of the dielectric susceptibilities.
13 citations