Topic
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: In this article, a second-order proper ferroelastic phase transition from the tetragonal rutile type to the orthorhombic calcium-chloride type structure is described.
Abstract: CaCl2 undergoes a second-order proper ferroelastic phase transition from the tetragonal rutile type to the orthorhombic calcium-chloride type structure atT
c
≈490 K. The transition is of the optical type and induced by an order parameter ofB
1g
symmetry. An underdamped soft mode exists above and belowT
c
, the frequency and intensity of which have been measured by Raman spectroscopy. Due to a strong coupling to strain the softening is incomplete and a transverse acoustical mode is predicted to become soft. The frequency of the optical soft mode, ωs, exhibits a classical Landau behavior in a remarkably large temperature range. The unusual value of the ratio of ∂ω
s
2
/∂ below and aboveT
c
of about −6.5 can be accounted for by appropriate terms of the thermodynamical potential. The Raman active hard modes show no significant anomaly atT
c
.
19 citations
TL;DR: The influence of Ce addition on the nature of phase transition in the La1−x¯¯ Ce x¯¯ Fe11.2Co0.7Si1.1 (x = 0, 0.1) alloy system has been investigated in this paper.
Abstract: The influence of Ce addition on the nature of phase transition in the La1−x
Ce
x
Fe11.2Co0.7Si1.1 (x = 0, 0.1) alloy system has been investigated. The substitution of Ce for La leads to a decrease of Curie temperature from 264 K to 254 K and to an increase of the maximum value of magnetic entropy change from 19.3 J/(kg K) to 21.5 J/(kg K). A detailed analysis of phase transition using Arrott plots, the Landau theory for order parameter and the construction of a universal scaling curve revealed that replacing 10 at.% La with Ce drives the magnetic transition from second-order to first-order and enhances a field-induced itinerant electron metamagnetic transition above T
C.
19 citations
TL;DR: In this article, a dual theory for three dimensional superconductor is derived starting from the lattice electrodynamics and studied by renormalization group, which predicts the divergence of the magnetic field penetration depth with the XY exponent, in contradiction to the results obtained from the Ginzburg - Landau theory for the superconducting order-parameter.
Abstract: A recently proposed form of dual theory for three dimensional superconductor is rederived starting from the lattice electrodynamics and studied by renormalization group. The superfluid density below and close to the transition vanishes as an inverse of the correlation length for the disorder field. The corresponding universal amplitude is given by the fixed point value of the dual charge, and it is calculated to the leading order. The continuum dual theory predicts the divergence of the magnetic field penetration depth with the XY exponent, in contradiction to the results obtained from the Ginzburg - Landau theory for the superconducting order-parameter. Possible reasons for this difference are discussed.
19 citations
TL;DR: It is shown that the polarization of d1T-MoS2 is robust to external electric fields and can be manipulated by the uniaxial strain and has dependence on both primary and secondary modes.
Abstract: The d1T-MoS2, distorted-1T group-VIB transition metal dichalcogenides monolayer, is considered as promising atomically thin out-of-plane ferroelectric materials. We study the origin of the ferroelectricity in d1T-MoS2 monolayer using first-principles calculations and the Landau theory of phase transition. In contrast to conventional improper ferroelectrics, we find that the polarization has dependence on both primary and secondary modes. It turns out that the charge imbalance between chalcogen atoms at different symmetry sites is the source for the out-of-plane polarization without any out-of-plane displacement in the primary mode. The secondary mode following the primary mode cancels partially the polarization and secures it against the depolarization field. We show that the polarization of d1T-MoS2 is robust to external electric fields and can be manipulated by the uniaxial strain.
19 citations
TL;DR: In this paper, a scaling formula of critical current density for anisotropic superconductors has been introduced on the basis of Ginzburg - Landau theory and the classical Kramer scaling law.
Abstract: A scaling formula of critical current density for anisotropic superconductors has been introduced on the basis of anisotropic Ginzburg - Landau theory and the classical Kramer scaling law. The model predicts the functional dependence of the critical current density on magnetic field and angle, and the functional relationship is in good agreement with experiments performed on thin films.
19 citations