International Journal of Modern Physics B

In order to investigate surface structure change due to phase transition, surface melting, surface segregation and thin film growth, we have developed a new system for reflection high-energy electron diffraction (RHEED) with two pairs of magnetic coils to measure rocking curves in short time. This system is the most suitable tool to determine the structure change with temperature in a wide range, and we studied the dynamical structure change during film growth of Si on Si(111) and the phase transitions of Si(111) and Si(100) surfaces at high temperature.

We defined normalized density operator that satisfies Liouville–von Neumann equation in terms of the invariant operator. The energy density inside the cavity decreased exponentially with time due to the conductivity of the media. We also evaluated the total number of photons in the cavity.

We present in this letter a realistic construction of the coherent states for the Morse potential using the Klauder–Perelomov approach. We discuss the statistical properties of these states, by deducing the Q- and P-distribution functions. The thermal expectations for the quantum canonical ideal gas of the Morse oscillators are also calculated.

A two-level crystal field model in the presence of the phonon field is considered. Spins are arranged on a lattice and weakly coupled to the lattice oscillations of small amplitudes. The anticommutator Green function perturbative method up to the second order in the coupling constant is applied to find thermodynamical quantities. The magnetic spectral function, describing the crystal field excitations, influences these quantities. The effect is studied numerically and illustrated in figures. In particular, the influence of the coupling on the Schottky specific heat is shown.

This paper presents the coherent elliptic states (CES) of alkaline constructed from the spherical Rydberg wavefunctions generated by the B-spline method associated with Hartree–Fock approximation. To construct the elliptic orbit for alkaline is not straightforward. The core effect plays an important role for the formation of elliptic states especially in higher and lower eccentricity. When the eccentricity is not large (i.e. e=0.6), the physical quantities of CES of alkaline atoms can be theoretically calculated by the replacement with hydrogen atom.

The extrapolation of finite-cluster calculations is used to examine ground-state properties of the one-dimensional Falicov–Kimball model with correlated hopping. It is shown that the correlated hopping strongly influences both the valence transitions and the conducting properties of the model and so it should not be neglected in the correct description of materials with correlated electrons. This is illustrated for two selected values of the Coulomb interaction that represent typical behavior of the model for small and intermediate (strong) interactions. In both cases the insulator–metal transitions (accompanied by continuous or discontinuous valence transitions) induced by correlated hopping are observed.

The large variety of the measured magnetic penetration depth is interpreted by using two microscopic gap models. We calculate the penetration depth of superconductor MgB₂ in low temperatures by using two gap and an anisotropic s-wave gap models. In the two gap model we consider that the total penetration depth is a weighted sum of the contribution from σ- and π-bands and the interaction between these two bands is ignored. The effect of impurities on the σ-band is less than that π-band and there are tremendous modifications of the temperature dependence of the penetration depth for π-band.

Under dielectric continuum approximation, by adopting the transfer matrix method, interface optical (IO) phonon modes and the Fröhlich electron–IO-phonon interaction Hamiltonian in a multilayer coaxial cylindrical quantum-well wire (QWW) were deduced and investigated. Numerical calculations on a four-layer GaAs/Al_xGa_1-xAs QWW have been performed. Results reveal that there are six branches of IO phonon modes. When the wave vector in z-direction k_z and the azimuthal quantum number m are small, the dispersion frequencies of IO modes sensitively depend on k_z and m. When k_z and m are relatively large, with the increasing of k_z and m, the frequency for each mode converges the limit frequency value of IO mode in single heterostructure, and the electrostatic potential distribution of each mode tends to be more and more localized at the interfaces, meanwhile, the coupling between the electron–IO-phonon becomes weaker and weaker. The calculation also shows that the phonon modes with higher frequencies have more significant contribution to the electron–phonon interaction. At last, it is found that k_z and m have analogous effects on the frequencies and the electrostatic potentials of the IO phonons.

Mechanism's effect of transversal magnetic field on the populations of excited states of He atoms has been investigated. Furthermore, the dependencies of complete absorption of He(I) spectral line transition 3³P_0,1,2–2³S₁ on optical plasma density are calculated by numerical methods taking into consideration the fine-structure and Zeeman splitting schemes of the spectral lines. Using the calculated values and experimental results, the dynamics of the populations of He(I) metastable states 2³S₁ of the He nanosecond discharge are discussed.

This article, considers in detail P. Gombás's idea of grouping electrons into n- and nl-shells in the Thomas–Fermi theory of free atoms briefly, the TFG n- and TFG nl-models respectively). Using these models, exact analytical expressions for the total energy E and the atomic form factor F(κ) are obtained. All integrals of the TFG nl-model are computed by means of the hypergeometric functions ₂F₁(x), ₃F₂(x), F₂(x,y) and F_A(x₁,…,x₆) for the first time. In particular, Weizsäcker's gradient correction to the kinetic energy of the nl-th shell generates a new numerical triangle with coefficients bw=n+2l(n-l-1).

Optical properties of thermally evaporated nickel phthalocyanine thin films have been characterised using spectrophotometric measurements of transmittance and reflectance in spectral range 200–2100 nm. The refractive index n and the absorption index k were calculated. Some of the optical absorption parameters, namely optical absorption coefficient (α), molar extinction coefficient (ε_molar), oscillator strength (f), electric dipole strength (q²) and absorption half bandwidth (Δλ) of the principal optical transitions have been also evaluated. The analysis of the spectral behaviour of the absorption coefficient (α), in the absorption region revealed indirect transitions. The fundamental and the onset energy gaps were estimated as 2.77±0.02 eV and 1.58±0.01 eV, respectively. According to the analysis of dispersion curves, the dielectric constants and dispersion parameters were obtained. The absorption measurements recorded in the UV–VIS region show two well defined absorption bands of phthalocyanine molecule, namely the Soret band (B) and the Q band. The Q band shows its characteristic splitting (Davydov splitting), and ΔQ was obtained as 0.21 eV. Discussion of the obtained results and their comparison with the previous published data are also given.