Landau theory

About: Landau theory is a research topic. Over the lifetime, 2882 publications have been published within this topic receiving 57078 citations.

Impact of radiation defects on the structural stability of pure zirconia

Abstract: Optical spectroscopy and x-ray diffraction were used to study the behavior of polycrystalline samples of pure monoclinic zirconia irradiated by low energy ions. A microscopic model based on these experiments is proposed to explain the displacive phase transition observed in this material after irradiation. Defects, produced in the oxygen sublattice, induce important strain fields on a nanometric scale. This strain field can be handled as a secondary order parameter within the Landau theory approach, leading to a decrease of the phase transition temperature and thus quenching the high temperature tetragonal phase. The model also explains the consequences of the thermal annealing for restoring the ground state monoclinic structure.

Nematic to isotropic transition in chemically disordered or multicomponent liquid-crystalline polymers

Abstract: A Landau theory is presented for the N-I transition of main-chain liquid-crystalline thermotropic statistical copolymers. We find a coupling between the conventional nematic (orientational) order parameter and a compositional order parameter that expresses nonuniformity in the density of flexible monomers. This coupling leads to a biphasic region at the N-I transition in accordance with the recent experiments of Stupp et al. Segregation by flexibility at the N-I transition is also analyzed for binary blends of thermotropic homopolymers

Optical Response of Sr 2 RuO 4 Reveals Universal Fermi-Liquid Scaling and Quasiparticles Beyond Landau Theory

Abstract: We report optical measurements demonstrating that the low-energy relaxation rate (1/τ) of the conduction electrons in Sr(2)RuO(4) obeys scaling relations for its frequency (ω) and temperature (T) dependence in accordance with Fermi-liquid theory. In the thermal relaxation regime, 1/τ ∝ (ħω)(2)+(pπk(B)T)(2) with p = 2, and ω/T scaling applies. Many-body electronic structure calculations using dynamical mean-field theory confirm the low-energy Fermi-liquid scaling and provide quantitative understanding of the deviations from Fermi-liquid behavior at higher energy and temperature. The excess optical spectral weight in this regime provides evidence for strongly dispersing "resilient" quasiparticle excitations above the Fermi energy.

Scalar Order: Possible Candidate for Order Parameters in Skutterudites

Abstract: Phenomenological Landau analysis shows that the properties of ordered phases in some skutterudites are consistently accounted for by a scalar-order parameter which preserves the cubic symmetry, even in the ordered phase. A universal value is found for the anisotropy ratio of the transition temperature in a magnetic field, homogeneous magnetization, and induced staggered magnetization. The difference in magnetic behavior between PrFe 4 P 12 and PrRu 4 P 12 near their phase transitions is explained within a single framework. For the low-field phase of PrFe 4 P 12 , the scalar order with Γ 1 g symmetry can explain (i) the absence of field-induced dipoles perpendicular to the magnetic field, (ii) isotropic magnetic susceptibility in the ordered phase, (iii) the field-angle dependence of the transition temperature, and (iv) the splitting pattern of the 31 P nuclear magnetic resonance (NMR) spectra. It is proposed how the order parameter in SmRu 4 P 12 is identified by NMR analysis of a single crystal.

The pressure-temperature phase diagram of BaTiO3: a macroscopic description of the low-temperature behaviour

Abstract: The pressure–temperature phase diagram of BaTiO3 has been investigated using a modification of the standard Landau potential to take account of quantum saturation of the order parameter at low temperatures. The calculated phase diagram agrees well with experiment for the cubic–tetragonal and tetragonal–orthorhombic transitions, but underestimates the orthorhombic–rhombohedral transition temperature somewhat. The saturation temperature (θS = 160 K) is sufficiently high that the expected critical point is not observed experimentally. Instead, each phase boundary bends sharply down, so each of the four crystalline structures of BaTiO3 has a stability field with increasing pressure at 0 K.