Modern Physics Letters B

One of the standard approaches to calculate the ground-state properties of strongly correlated electronic systems is to use a Jastrow–Slater wavefunction as a starting point. When considering confined electrons in a two-dimensional parabolic quantum dot, one chooses the Slater determinant to be the ground-state wavefunction of confined independent electrons and then determines the form of the Jastrow correlation factor in a way that incorporates accurately the spatial correlations of the system. One way to choose a quality Jastrow correlation factor is to consider the two-body problem and search the best possible yet simple approximative solution to such a problem. To achieve this goal, we consider the two-body problem of confined electrons interacting with a Coulomb repulsive potential in zero magnetic field and focus on their relative motion. Based on straightforward theoretical considerations, we suggest a simple two-body Jastrow correlation factor that optimizes very well the overall trial energy. We test the quality of the proposed Jastrow correlation factor by comparing the results to exact numerical diagonalization solutions.

We have performed first-principle full-potential (linear) augmented plane wave plus local orbital calculations (FP-L/APW + l₀) with density functional theory (DFT) in local density approximation (LDA) and generalized gradient approximation (GGA), with the aim to determine and predict the electronic and optical properties of rocksalt BaO, BaS, BaSe, BaTe and BaPo compounds. First we present the main features of the electronic properties of these compounds, where the electronic band structure shows that the fundamental energy gap is indirect (Γ–X) for all compounds except for BaO which is direct (X–X). The different interband transitions have been determined from the imaginary part of the dielectric function. The real and imaginary parts of the dielectric function and the reflectivity are calculated. We have presented the assignment of the different optical transitions existing in these compounds from the imaginary part of the dielectric function spectra with respect to their correspondence in the electronic band. We have also calculated the pressure and volume dependence of the optical properties for these compounds.

Thermal entanglement is investigated in a two-qubit Heisenberg XY model with different inhomogeneous magnetic fields. It is found that the entanglement is dependent on the magnetic field, and the magnetic fields along different axes have different control efficiencies of entanglement. In addition, no matter in antiferromagnetic model or in ferromagnetic model, according to the relation between spin–spin coupling coefficients, the more efficient control parameters of entanglement can be obtained by adjusting the direction of external magnetic fields.

Experimentally, a maximum point in the curve of the saturated property ψ=(1-T_r)P_r versus the saturated temperature was postulated (High Temp.-High Press.26 (1994) 427). Here, T_r is the saturated temperature reduced by the critical temperature and P_r is the saturated pressure reduced by the critical pressure. Later, this behavior was applied to assure the saturated vapor pressure critical amplitudes (Appl. Phys. Lett.90 (2007) 141905). In this paper, we indicate that theory of equation of state (EOS) can predict this maximum point. The EOSs we study are the combinations of the hard sphere repulsions and some normally used attractions such as the Redlich–Kwong attraction. We find the EOSs with Redlich–Kwong attractive terms give out the results in the experimental range.

Ni-rich intermetallic compound Ni₃Al films were deposited using the dual-target magnetron co-sputtering method. The grain-boundary and grain-size characteristics of the as-deposited and post-annealed Ni₃Al films were investigated using a slow positron beam. The results demonstrate a distinct change of S-parameter and positron effective diffusion length L_eff values as samples were annealed at different ambient atmospheres and temperatures. It shows that the positron trapping center is mainly associated with intergranular vacancies, and changes to either the vacancy cluster size or the grain size have been invoked to explain the changes of the values of the S-parameter and L_eff. Ni-rich oxygen-Ni₃Al films were also studied. All films were identified using X-ray diffraction and the results confirm the conclusion obtained by the slow positron beam.

Temperature dependence of magnetization for the composite La_0.67Ca_0.33MnO₃ (LCMO)/xCuO (x = 20%) has been measured in the cooling and warming process under magnetic fields of 0.5 T and 5.0 T. Unusual magnetic hysteresis behavior was observed, which is different from the spin glass behavior usually observed in perovskite manganites. It is interesting to note that in the same temperature region, the sample shows substantial magnetoresistance effect, and a relaxation behavior of resistivity has also been observed. Moreover, the ρ–T curve for the sample fits well to the phenomenological percolation model based on phase segregation. This result confirms the coexistence of ferromagnetic clusters and paramagnetic regions near T_c.

This paper studied the mechanical and chemical properties of hydroxyl apatite (HA) crystal structure in the teeth when human molars were soaked in slight acid solution. First, we soaked the ground and polished molars respectively in the liquor of 30 wt.% H₂CO₃ and the liquor of 30 wt.% H₂O₂ for 10, 20, or 60 minutes. Next, we used a nanoindenter to measure the hardness and Young's modulus. Finally, we used a scanning electron microscope (SEM) coupled with energy dispersive spectroscopy (EDS) to analyze the variation of Ca, P and Na in teeth, a high resolution transmitting electron microscope (HRTEM) to observe the arrangement of crystallization phase of HA, and X-ray diffraction (XRD) to analyze the crystallinity of the hexagonal phase of HA. The results showed that the demineralization phenomenon of the calcium–phosphorous compound in teeth made the teeth reduce sharply in hardness and Young's modulus after they were soaked in the two slight acid solutions for 10 minutes, but the re-mineralization phenomenon made the hardness and Young's modulus ascend gradually when the time lasted longer. With the same period of time, the teeth soaked in H₂CO₃ were lower in the hardness and Young's modulus than that in H₂O₂.

A theoretical model is presented to study the effect of an external magnetic field on antiferromagnetic (AFM) order parameter and Neel temperature in electron doped high T_C cuprates in normal state. The expression for the antiferromagnetic order parameter is derived by using double time electron Green function of Zubarev type and studied numerically. It is found that the magnetic field up to a certain parametric value considerably enhances the Neel temperature. Above this value, the Neel temperature decreases on increasing the field. The trend of field dependence of the AFM order parameter at 30 K is quite similar to that of Neel temperature. This parametric study of external magnetic field is in good agreement with experimental findings.

Erythrosine B based poly (methacrylate) films with varying even number of methylene spacers have been prepared by the free radical polymerization method. All optical switching and beam deflection effects of polymer films have been investigated by using Nd:YAG laser (532 nm) as a pump beam and a He–Ne laser (632.8 nm) as a probe beam. The nonlinear refractive indices of polymer films are determined using the Z-scan technique. The optical switching and beam deflection effects are due to the change of the refractive index of polymer under the pump beam. The experimental results show that erythrosine B based poly (methacrylate) films have potential application in optical switching.

The purpose of this study is to implement a new analytical method (the DTM-Padé technique, which is a combination of the differential transform method (DTM) and the Padé approximation) for solving Navier–Stokes equations. In this letter, we will consider the DTM, the homotopy perturbation method (HPM) and the Padé approximant for finding analytical solutions of the three-dimensional viscous flow near an infinite rotating disk. The solutions are compared with the numerical (fourth-order Runge–Kutta) solution. The results illustrate that the application of the Padé approximants in the DTM and HPM is an appropriate method in solving the Navier–Stokes equations with the boundary conditions at infinity. On the other hand, the convergence of the obtained series from DTM-Padé is greater than HPM-Padé.

Indium tin oxide (ITO) films were deposited on glass substrate without external heating by DC magnetron sputtering with continuous deposition of 800 s (S1) and discontinuous depositions of 400 s × 2 times (S2), 200 s × 4 times (S3) and 100 s × 8 times (S4). The structural, surface morphology, optical transmittance and electrical resistivity of ITO films were measured by X-ray diffraction, atomic force microscope, spectrophotometer and four-point probe, respectively. The deposition process of the S1 condition shows the highest target voltage due to more target poisoning occurrence. The substrate temperature of the S1 condition increases with the saturation curve of the RC charging circuit while other conditions increase and decrease due to deposition steps as DC power turns on and off. Target voltage and substrate temperature of ITO films decrease when changing the deposition conditions from S1 to S2, S3 and S4, respectively. The preferential orientation of ITO films were changed from dominate (222) plane to (400) plane with the increasing number of deposition steps. The ITO film for the S4 condition shows the lowest electrical resistivity of 1.44 × 10^-3 Ω·cm with the highest energy gap of 4.09 eV and the highest surface roughness of 3.43 nm. These results were discussed from the point of different oxygen occurring on the surface ITO target between the sputtering processes which affected the properties of ITO films.

Coherent potential approximation (CPA) is extended to a two-band model for diluted magnetic semiconductors (DMS). The magnetic transition temperature T_c as a function of magnetic coupling constants, hopping parameters and carrier densities is calculated by minimizing the free energy of the coupled carrier-localized spin system. It is shown that T_c can be substantially raised by considering multiband systems.