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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: Using Landau theory, the possibility that hexagonal structures can exist in cholesteric liquid crystals in an applied field is considered and it is found that two- and three-dimensional hexagonal phases are thermodynamically stable in different regions of the chirality-temperature field phase diagram when the anisotropy is positive.
Abstract: Using Landau theory, the possibility that hexagonal structures can exist in cholesteric liquid crystals in an applied field is considered. Both positive and negative dielectric anisotropy systems are studied. It is found that two- and three-dimensional hexagonal phases are thermodynamically stable in different regions of the chirality-temperature field phase diagram when the anisotropy is positive, while for negative anisotropy only a three-dimensional phase occurs. This is in agreement with experimental data. In addition, the theoretical results indicate that two different three-dimensional hexagonal phases, having the same space group (P${6}_{2}$22) but different structure factors, can exist when the anisotropy is positive. Ways of verifying this prediction by optical or NMR studies are considered. Finally, the topological aspects of disclinations in the hexagonal phases are considered. Each of the four stable hexagonal structures is found to have two uniaxial positive and one uniaxial negative defect line. The latter is the only topological disclination when the order parameter is taken to be a uniaxial director rather than a biaxial symmetric tensor.

28 citations

Journal ArticleDOI
TL;DR: In this article, the magnetic measurements show a clear paramagnetic-ferromagnetic transition with a large magnetic entropy change over a wide range of temperature and conductivity analysis indicates that the investigated compound exhibits a semiconductor behavior.

28 citations

Journal ArticleDOI
TL;DR: In this paper, the cyclic temperature and stress-induced martensitic transformations (MTs) of Ni-Mn-Ga single-crystal alloy with c/a < 1 have been studied both experimentally and theoretically.

28 citations

Journal ArticleDOI
TL;DR: In this paper, the authors determine the nature of the magnetic order on the surface of a topological insulator (TI) which develops due to hexagonal warping and the resulting Fermi surface nesting in the presence of a repulsive Hubbard interaction.
Abstract: We determine the nature of the magnetic order on the surface of a topological insulator (TI) which develops due to hexagonal warping and the resulting Fermi surface (FS) nesting in the presence of a repulsive Hubbard interaction. For this purpose we investigate the spin susceptibility and derive a Landau theory to compare the different accessible phases. For a nearly hexagonal FS and sufficiently strong interaction the magnetic ground state is formed by a skyrmion lattice, i.e., by a superposition of three helical spin density waves which preserves C$_3$ symmetry. The magnetic ground state is topologically nontrivial with a nonzero skyrmion charge, which can be stabilized and controlled by an applied magnetic field. By bringing the TI in proximity to a conventional superconductor one can engineer a C$_3$-symmetric topological superconductor. We explore the modification of the phase diagram as well as the mutual influence between the skyrmion structure and a multipolar distribution of supercurrents, which can provide information about the underlying skyrmion charge.

28 citations

Journal ArticleDOI
TL;DR: In this paper, a study of the dielectric behaviour of TGS revealed an anomalous temperature dependence of the nonlinear coefficients and a model calculation was given to explain the deviations from the normal behaviour.
Abstract: A study of the dielectric behaviour of TGS revealed an anomalous temperature dependence of the nonlinear coefficients. A model calculation is given to explain the deviations from the normal behaviour. The thermodynamic behaviour of TGS is consistent with the Landau theory if one does not assume temperature independent nonlinear coefficients.

28 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202317
202242
202142
202041
201949
201855