Landau theory of phase transitions in thick films

A simple expression is used for the free energy density with a one-component order parameter, and the boundary conditions at the surfaces of a film of thickness L are given by means of an extrapolation length δ. Exact expressions are given for the critical temperature and the order parameter profile in terms of elliptic functions, and the nature of the phase transition is discussed.     

Landau theory of shape phase transitions in the cranked interacting boson model

Landau theory of phase transitions is applied to quadrupole shapes of rotating atomic nuclei within the interacting boson model (IBM) with cranking. It is shown that the coherent-state method must be generalized to allow for non-Hermitian quadrupole tensors of the coherent-state coefficients, which results in important modifications of the cranking shape-phase diagram compared to previous non-IBM studies of rotating nuclei. The parameter space has two surfaces of the first-order phase transitions and a curve of the second-order phase transition at their intersection. The phase structure of the cranked IBM closely resembles systems with competing superconducting and normal phases.     

Laser threshold and nonlinear Landau fluctuation theory of phase transitions

The threshold region for a single mode laser is treated by Landau's theory of order parameter fluctuations. Taking into account a kinetic energy in the Landau functional, approximate equations of motion for the laser field are derived which include coupling of phase and amplitude. From these it is easy to get the correlation functions and linewidths for intensity and field as well as the transient behaviour of intensity throughout the nonlinear transition region. In addition, a dynamical decoupling scheme of noise theory is applied to calculate the same quantities. Although these methods are very simple the results agree fairly well with those of the much more involved Fokker-Planck theory.     

On the possibility of temperature-induced order-order transitions in the Onyszkiewicz metamagnetic model

The Onyszkiewicz model for temperature-induced metamagnets (OTIM model) is redefined on a bipartite lattice of Ising spins. The ground-state diagrams for the square and simple-cubic lattices are presented. The OTIM model is proved to exhibit temperare-induced transitions between ordered phases in some (relatively narrow) range of model parameters.     

Drug binding and order-order and order-disorder transitions in DNA triple helices

The Zimm and Bragg theory for helix-to-coil transitions has been suitably amended and applied to explain the two-step transition in the DNA triplex. The experimental measurements reported elsewhere have been successfully interpre- ted. The order-order and order-disorder transitions associated with the melting of the DNA triple helix, with and without netropsin binding, were characterized by the nucleation parameter, enthalpy change, sharpness of transition, and heat capacity. The destabilization of the triplex and stabilization of the duplex on netropsin binding are reflected in these characteristic parameters.     

Domain effects near the order-disorder and order-order ferromagnetic transitions in Gd and Dy

The technique of transient enhancement of the ac initial susceptibility χ has been used to compare domain effects in the ferromagnetic-paramagnetic transition of Gd and the ferromagnetic-antiferromagnetic transition of Dy. The temperature hysteresis in both χ and enhanced χ in the AF region of Dy indicates the existence of domains. The results for Dy support the suggestion that the transition from ferromagnetic to antiferromagnetic order upon warming in the vicinity of the Curie temperature takes place via an intermediate, moment-bearing domain structure.     

Algebraic investigations in Landau model of structural phase transitions

Czechoslovak Journal of Physics -     

Spectroscopy of Landau transitions of two-dimensional electron gases

We have employed resonant inelastic light scattering spectroscopy to study electronic transitions in multilayer two-dimensional electron gases in magnetic fields of 4–14 T. From polarized spectra, we have evidence for both single particle Landau transitions (Δl = 1 and Δl = 2) as well as their collective counterparts. We show the variation of intensities with B and the resonant behavior, but are unable to identify a scattering mechanism.     

A Landau theory of the Peierls-BCS transition

We introduce a Landau type theory of the Peierls instability-superconductor transition involving two complex order parameters. Under a particular inequality condition among expansion parameters, the theory predicts that the superfluid conductivity should vary as $\text{(T?T}{}_{\mathrm{<mtext>c</mtext>}}\text{)}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$ above the critical region and as $\text{(T}{}^1{}_{\mathrm{<mtext>c</mtext>}}\text{?T)}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$ below the critical region.     

Landau theory of the isotropic-nematic critical point

Landau theory is used to analyze the effect of an applied on nematics with positive dielectric (or diamagnetic) anisotropy. Analytic results are given for the phase boundary, stability limits, and location of the critical points in the field-temperature phase diagram. For biphenyl compounds having a dielectric anisotropy ?_a≈10, it is argued that the critical point should occur at E_c≈10² kV/cm, which is experimentally accessible.     

Landau transitions at higher gaps in InSb and GaSb

Landau levels have been resolved at the E₁ + Δ₁ gap in InSb and at the E₁ edge in GaSb. Transverse reduced masses of 19 ± 3 and 21.4 ± 1.5 have been obtained at the respective edges. Using band gaps determined from the experiment, the spin-orbit splitting Δ₁ has been measured as 0.500 ± 0.013 eV in InSb. Combined with a measurement of the zone center spin-orbit splitting, this gives a ratio of 0.623 ± 0.02 of slightly less than $\text{2}\text{3}$.     

Homogeneous-inhomogeneous transitions in a Landau level with spin splitting

The homogeneous-inhomogeneous transitions of a two-dimensional electron gas in a strong perpendicular magnetic field are studied in the particular case when half of the states in a spin splitted Landau level are occupied. To this end the dielectric susceptibility in the homogeneous states as well as the free energy in the modulated states are calculated. Unless theg factor dos not exceed a certain value the charge-density waves are stable in an interval of finite temperatures.