International Journal of Modern Physics B

We consider a two-leg S=1/2 quantum spin ladder model with two-spin (intra-rung) and four-spin (inter-rung) Heisenberg exchange interactions and a uniform magnetic field. Exact mappings are derived connecting the partition function and correlations in the three-parameter quantum model to those known in a two-parameter Ising chain. The quantum phase diagram of the ladder magnet is determined. Static correlations provide pertinent correlation lengths and underlie spatial fluctuation behaviors at arbitrary temperatures, including quantum fluctuations at absolute zero. Dynamic correlations in zero field are used to obtain an exact solution for the inelastic neutron scattering function S^xx(q, ω) at all temperatures, explicitly yielding the elementary excitation spectrum.

We studied the entangled two-qubit nonorthogonal pure states through spin coherent states. Using the concurrence as a measure of entanglement we express it as a function of the amplitudes of those states and find conditions for maximal and minimal entanglement.

Following the theoretical prediction of ferromagnetism in Mn- and Co-doped ZnO, there has been an immense experimental search for dilute semiconductors that show ferromagnetic ordering above room temperature, and several workers have reported ferromagnetism in bulk samples as well as in thin films of these materials. Mn-doped ZnO is the key material in this regard, which has been, in the recent past, shown to exhibit such magnetic properties. Many more such attempts have either led to failure or to a much lower T_c, and there have been a lot of confronting reports casting considerable doubts on the magnetism in this system. In order to shed some light, we have prepared and characterized dilute Mn-doped (2 and 4%) ZnO pellets. SQUID measurements confirm that the 2% sample shows above room temperature ferromagnetic ordering, the ferromagnetic contribution coming mainly from the bulk. The ordering gets completely quenched for 4% Mn doping. Upon cooling down, the 2% Mn doped sample showed further enhancement in magnetic properties appreciably. On the other hand, the 4% sample did not show any ferromagnetic ordering, even down to 5 K, and has been found to retain the paramagnetic character.

This article deals with the connection between multipole matrix elements <nl|r^β|n'l' >_ν for H-like atoms and new properties of Appell's function F₂(x,y) to the vicinity of the singular point (1, 1), where ν is the so-called "auxiliary" parameter of Heun-Schrödinger's radial equation, |1 - ν| = o(1), is the "effective" nuclear charge. Exact numerical values for the dipole matrix elements, the average oscillator strengths, the transition probabilities and the line intensities, as n ≤ 4 and n' ≤ 10, in the form of regular rational fractions are given (in Tables 1–4), that make more precise the well-known Tables 13–16 by Hans A. Bethe.

The effect of spatial dielectric screening on the diamagnetic susceptibility (χ_dia) of a donor in Low Dimensional Semiconducting Systems like Quantum Well, Quantum Well Wire and Quantum Dot in the infinite barrier model has been computed and investigated within the effective mass theory using variational method. We observe that the effect of spatial dielectric screening on χ_dia decreases with decrease of dimensionality of the system.

First-principles calculations based on density functional theory (DFT) within the generalized gradient approximation (GGA) have been carried out to study the migration of helium in tungsten. The results show that helium interstitial jump directly between two tetrahedral sites with very low migration energy. The migration manner of interstitial He is related to the configuration of the host metal. Furthermore, the dissociation energy of a substitutional helium atom from a vacancy has been calculated from first-principles.

We propose a scheme of swapping between two pairs of nonorthogonal entangled coherent states using a beam splitter, two phase shifters and photon counting measurements. We find that an almost perfect swapping is possible for an appreciable mean number of photons.

In this study, the effect of bismuth content on the crystal structure and morphology of bismuth silicate (BSO:Bi₄Si₃ O₁₂) polycrystals were investigated with X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). BSO materials have been successfully prepared by the solid-state reaction. The BSO phase was crystallized at 950°C for 12 h. In summary, 10% of excess bismuth was found to be the optimum composition with respect to crystallization, morphology, and grain size.

Based on the analysis on the characteristics of the KdV equation, Kuramoto-Sivashinsky equation and KdV-Burgers-Kuramoto equation, a combination method is proposed to construct the explicit exact solutions for the KdV-Burgers-Kuramoto equation by combining with those of the KdV equation and Kuramoto-Sivashinsky equation. As a result, many explicit exact solutions to the KdV-Burgers-Kuramoto equation are successfully derived by this approach.

A variational calculation is given within the effective mass approximation of the binding energy of a hydrogenic donor impurity located on the axis of an infinitely long circular quantum well wire. A uniform magnetic field is applied along the axis of the wire. The different effective masses of the wire and the barrier are taken into consideration. This has not been done hitherto in the presence of the magnetic field. New analytical expressions for the electron energy levels and the binding energies of the hydrogenic impurity in the ground and the first four excited states have been derived.

Moreover, the form of the binding energy reported in earlier works in the special case of zero magnetic field has been amended. A new form of the trial wavefunction has also been introduced. It has the advantage of satisfying the required boundary conditions in the case of different masses of the wire and barrier, and thus it resembles the exact solution in this respect. The new form of the trial wavefunction has been applied to the case of the ground state. It has improved the results of binding energy considerably as they tend to approach the exact solution from below.

In this study, the photoionization cross-section and oscillator strength for the intersubband electronic transitions associated with an on-center impurity in the ZnS/SiO₂ spherical quantum dot have been calculated. The effects of dot radius, the normalized photon energy and the potential barrier height on the cross-section have been investigated. In the calculations, both the infinite and finite confinement cases have been considered.

Using a thermodynamic model based on the generalized Landau free-energy density expansion, we investigate the influence of hydrostatic pressure on the spontaneous polarization and tilt angle of ferroelectric chiral smectic C (Sm C^*) phase near the Sm A–Sm C^* transition in a ferroelectric mesogen DOBAMBC. It is shown that the pressure dependence of the tilt angle, spontaneous polarization and Sm A–Sm C^* transition temperature (T_c) can be described in terms of four pressure-dependent Landau coefficients: two achiral coefficients a and b and two chiral coefficients Λ and d. The pressure dependence of the parameter a is due to the pressure-dependent T_c. With the increasing pressure, the stability of the Sm C^* phase decreases. A close agreement between theory and experiment is found.