International Journal of Modern Physics B

A new mean field statistical mechanics model of two interacting groups of spins is introduced, and the phase transition is studied in terms of their relative size. A jump of the average magnetization is found for large values of the mutual interaction when the relative percentage of the two populations crosses a critical threshold. It is shown how the critical percentage depends on internal interactions and on the initial magnetizations. The model is interpreted as a prototype of resident-immigrant cultural interaction, and conclusions from the social sciences perspectives are drawn.

Two different results concerning the elastic behavior of the heterogeneous worm-like chain (WLC) [D. Bensimon et al., Europhys. Lett.42, 97 (1998)] and rod-like chain (RLC) [P. Nelson, Phys. Rev. Lett.80, 5810 (1998)] are compared. We argue that the RLC is a more suitable model for double-stranded (ds-) DNA. As the hetero-RLC is the basic model for studying sequence-dependent ds-DNA, a rigorous path integral analysis for the effective bending persistence length is performed in the weak disorder limit. The novelty of the paper is in analyzing a path integral on the Lie group SO(3) with random forcing, which supplies a rigorous basis for the analysis of RLC type models.

Following a recent work [Gál, Phys. Rev. A64, 062503 (2001)], a simple derivation of the density-functional correction of the Hartree–Fock equations, the Hartree–Fock–Kohn–Sham equations, is presented, completing an integrated view of quantum mechanical theories, in which the Kohn–Sham equations, the Hartree–Fock–Kohn–Sham equations and the ground-state Schrödinger equation formally stem from a common ground: density-functional theory, through its Euler equation for the ground-state density. Along similar lines, the Kohn–Sham formulation of the Hartree–Fock approach is also considered. Further, it is pointed out that the exchange energy of density-functional theory built from the Kohn–Sham orbitals can be given by degree-two homogeneous N-particle density functionals (N = 1, 2, …), forming a sequence of degree-two homogeneous exchange-energy density functionals, the first element of which is minus the classical Coulomb-repulsion energy functional.

In the present paper, the problem of two-dimensional static deformation of an isotropic elastic half-space of irregular thickness has been studied using the eigenvalue approach, following a Fourier transform. The irregularity is expressed by a rectangular shape. As an application, the normal line-load acting inside an irregular isotropic half-space has been considered. Further, the results for the displacements have been derived in the closed form. To examine the effect of irregularity, variations of the displacements with horizontal distance have been shown graphically for different values of irregularity size, and they are compared with those for the medium with uniform shape. It is found that irregularity affects the deformation significantly.

The transmission probability and the persistent currents in crossing a double-ring system with an impurity are investigated theoretically. The dependence of persistent currents on the sizes of the rings and the influence of the impurity on the transmission and persistent currents are shown. One finds that the impurity potential may help the enhancement of current magnification in a certain range of Fermi energies. Moreover, the persistent currents can be modulated by adjusting the impurity potential.

Dielectric relaxation spectroscopy in the frequency range 50 Hz to 1 MHz has been carried out in a room temperature ferroelectric liquid crystal mixture in the SmC*, SmA and N* phases in cells of different thickness. The relaxation frequency f_r, distribution parameter α and dielectric strength δ∊ have been evaluated. Goldstone mode, domain mode and soft mode have been observed. It is found that the cell thickness has a significant effect on the dielectric parameters of the ferroelectric liquid crystal material. The results have been discussed.

Aluminum antimonide (AlSb) is thought to be a potential material for high efficiency solar cells. In this paper, AlSb thin films have been fabricated by DC magnetron sputtering on glass substrates. The sputtering target consists of aluminum and antimony, and the area ratio of Al to Sb is 7:3, which is derived from research into the relationship between the deposition rates of both the metals and sputtering power. XRD and AFM measurements show that the as-deposited films are amorphous, but become polycrystalline with an average grain size of about 20 nm after annealing in an argon atmosphere. From optical absorption measurements of annealed AlSb films, a band gap of 1.56 eV has been demonstrated. Hall measurements show that the films are p-type semiconductors. The temperature dependence of dark conductivity tested in vacuum displays a linear lnσ to 1/T curve, which indicates a conductivity activation energy of around 0.61 eV.

A three square well model is developed, which allows one to easily calculate the correlation between the coupling strength parameters and superconducting transition temperature (T_c), pressure and volume derivative of T_c and isotope effect exponent for MgB₂. Upon considering the three interactions, namely, electron-phonon, electron-plasmon and Coulomb, the analytical solutions for the energy gap equation allow us to understand the relative interplay of these interactions. The values of the coupling strength and of the Coulomb interaction parameter indicate that the superconductor is in the intermediate coupling regime. The superconducting transition temperature of MgB₂ for the 2D band is estimated as 41 K for and μ^σ*≈0.28. We present correlation curves of T_c with various coupling strengths as electron-phonon , electron-plasmon and the Coulomb screening parameter (μ^σ*). The present approach also explains the reported boron isotope effect and the pressure derivative of T_c in the test material. We suggest from these results that both the plasmons and phonons within the framework of a three square well scheme consistently explain the effective electron-electron interaction leading to superconductivity in MgB₂. The implications of the effective interactive potential with both σ and π carriers and its analysis are discussed.

The electrical characteristics of Cr/p–Si(100) Schottky barrier diodes have been measured in the temperature range of 100–300 K. The I-V analysis based on thermionic emission (TE) theory has revealed an abnormal decrease of apparent barrier height and increase of ideality factor at low temperature. The conventional Richardson plot exhibits non-linearity below 200 K with the linear portion corresponding to activation energy 0.304 eV and Richardson constant (A^*) value of 5.41×10^-3 Acm^-2 K^-2 is determined from the intercept at the ordinate of this experimental plot, which is much lower than the known value of 32 Acm^-2K^-2 for p-type Si. It is demonstrated that these anomalies result due to the barrier height inhomogeneities prevailing at the metal-semiconductor interface. Hence, it has been concluded that the temperature dependence of the I-V characteristics of the Cr/p–Si Schottky barrier diode can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights. Furthermore, the value of the Richardson constant found is much closer than that obtained without considering the inhomogeneous barrier heights.

The electrical properties of alizarin doped anthraquinone were investigated using a complex impedance spectroscopy technique. Dielectric study revealed a phase transition from the semiconducting to the conducting state at 53°C. The dielectric relaxation was found to be of non-Debye type. Evidence of temperature-dependent electrical relaxation phenomena as well as a positive temperature coefficient of conductivity character were observed in the sample. The frequency dependence of AC conductivity data followed a power law. Electric modulus as well as AC conductivity analyses indicated the possibility of a hopping mechanism for electrical conduction in the system. The activation energy and minimum hopping distance were estimated from the AC conductivity data.