International Journal of Modern Physics B

We put forward a scheme on how to generate entangled state of Bose–Einstein condensate (BEC) using electromagnetically induced transparency (EIT). It is shown that we can rapidly generate the entangled state in the dynamical process and the entangled state maintained a long time interval. It is also shown that the better entangled state can be generated by decreasing coupling strengths of two classical laser fields, increasing two-photon detuning and total number of atoms.

In this paper, we investigate the tunable characteristics of shock waves propagating in one-dimensional magnetic granular chains at various chain lengths and magnetic flux densities. According to the Hertz contact theory and Maxwell principle, a discrete element model with coupling elastic and field-induced interaction potentials of adjacent magnetic grains is proposed. We also present hard-sphere approximation analysis to describe the energy partitioning features of magnetic granular chains. The results demonstrate that, for a fixed magnetic field strength, when the chain length is greater than two times of the wave width of the solitary wave, the chain length has little effect on the output energy of the system; for a fixed chain length, the shock absorption and energy partitioning features of magnetic granular chains are remarkably influenced by varying magnetic flux densities. This study implies that the magnetic granular chain is potential to construct adaptive shock absorption components for impulse mitigation.

The two-dimensional electron gas (2DEG) mobilities limited by alloy disorder (AD) scattering in both Ga- and N-polar AlGaN/GaN heterostructures are investigated. It was found that the AD scattering limited electron mobility in N-polar heterostructures is on the order of 10³–10⁴ cm²/Vs, which is comparable to the optical phonon scattering at room-temperature. In comparison, the AD scattering in Ga-polar samples is much less important. Moreover, the electron mobility decreases with the 2DEG density in the Ga-polar device but shows a reverse trend in the N-polar counterpart. This is found to be caused by the rather different electric field distributions in Ga- and N-polar AlGaN/GaN heterostructures. In addition, we find that an AlN interlayer can effectively reduce the alloy scattering, mainly due to the large band offset between AlN and GaN. The calculated mobilities have been compared with the experiment results and good agreements are found. We believe that our results are important for the design of AlGaN/GaN heterostructure-based devices, especially the N-polar ones.

Silicon quantum dots (Si-QDs) embedded B-doped SiN${}_x$ films were fabricated by magnetron co-sputtering. The effects of B content on the structural, optical and electrical properties of the films were studied. The study found that the amount of B dopant has no significant effect on the crystallization characteristics of the films. B atoms may be doped in the Si-QDs or exist in the silicon nitride or the interface between Si-QDs and the matrix. PL intensity increases with increasing B content, but increases at first and then decreases. The conductivity as a function of the dopant concentration increases at first from a value of 2.71 × 10${}^{-4}$ S/cm to 5.83 × 10${}^{-2}$ S/cm until 0.9 at.% and then decreases. By employing B-doped Si-QDs films, Si-QDs/c-Si heterojunction solar cells were fabricated and the effect of B doping concentration on the photovoltaic properties was studied. It was found that, with the increase of B doping amount, the photovoltaic performance is improved, when the B doping amount is 0.9 at.%, the efficiency reaches the highest value of 4.26%.

In this paper, we explore the structural, electronic, thermoelectric and elastic properties of intermetallic compounds ScTM (TM = Cu, Ag, Au and Pd) using density functional theory. The produced results show high values of Seebeck coefficients and electrical conductivity for these materials. High power factor for these materials at room-temperature shows that these materials may be beneficial for low-temperature thermoelectric devices and alternative energy sources. Furthermore, elastic properties of these compounds are also calculated, which are used to evaluate their mechanical properties. The Cauchy’s pressure and B/G ratio figure out that these compounds are ductile in nature. The calculated results also predict that these compounds are stable against deforming force.

FEA method is applied in order to investigate the bandgaps of two-dimensional (2D) phononic crystals which are composed with self-similarity hollow inclusions. Transmission spectra together with dispersion relations and displacement fields have been studied with FEA in detail. The simultaneous mechanisms of Bragg scattering enable multiterm bandgaps to be unfolded by the structure that can be effectively shifted by changing the lattice constant, matrix density and degree of self similarity. The smallest bandgap is located in the infrasonic wave range. Our results verify these phononic crystals with self-similar hollow inclusion structure which can change the number, location and width of bandgaps.

The effect of the electron–phonon interaction on an electron bound to a hydrogenic impurity in a three-dimensional (3D) anisotropic quantum dot (QD) is studied theoretically. We use the Landau–Pekar variational approach to calculate the binding energy of ground state (GS) and first-excited state (ES) with considering electron–phonon interaction. The expressions of the GS and ES energies under investigation depict a rich variety of dependent relationship with the variational parameters in three different limiting cases. Numerical calculations were performed for ZnSe QDs with different confinement lengths in the xy-plane and the z-direction, respectively. It is illustrated that binding energies of impurity polarons corresponding to each level are larger in small QDs. Furthermore, the contribution to binding energy from phonon is about 15% of the total binding energy.

In this paper, we study the effect of the number of wells, inner (R${}_{\mathrm{\text{in}}}$) and outer (R${}_{\mathrm{\text{out}}}$) quantum ring radiuses, and magnetic field as controlling tools to change the nonlinearity in optical properties of GaN/AlN constant radius multi-layer quantum dots and rings. It is seen that for small R${}_{\mathrm{\text{out}}}$ and for fixed R${}_{\mathrm{\text{in}}}$ and R${}_{\mathrm{\text{out}}}$, by increasing the number of wells, the nonlinearity increases, while for greater R${}_{\mathrm{\text{out}}}$ and for fixed R${}_{\mathrm{\text{in}}}$ and R${}_{\mathrm{\text{out}}}$, by increasing the number of wells the nonlinearity first decreases and then increases. For systems with greater R${}_{\mathrm{\text{in}}}$, the nonlinearity continually increases by increasing the number of wells. For fixed R${}_{\mathrm{\text{out}}}$, the critical well number, in which the nonlinearity changes its behavior, decreases by increasing the inner quantum ring radius R${}_{\mathrm{\text{in}}}$. The absorption coefficient does not undertake any blue or red shifts by changing the number of wells. In the systems with more number of wells, the nonlinearity reduces more rapidly by increasing the magnetic field. Finally, by increasing the radius R${}_{\mathrm{\text{out}}}$, the nonlinearity increases.

We find approximate solutions for the two-dimensional nonlinear $\mathrm{\Sigma }$-model with Dzyalioshinkii–Moriya term, representing magnetic Skyrmions. They are built in an analytic form, by pasting different approximate solutions found in different regions of space. We verify that our construction reproduces the phenomenology known from numerical solutions and Monte Carlo simulations, giving rise to a Skyrmion lattice at an intermediate range of magnetic field, flanked by spiral and spin-polarized phases for low and high magnetic fields, respectively.

In this work, we looked into the lowest energy structures of small lithium clusters (Li_n, n = 5, 6, 7, 8) utilizing conventional PBE exchange–correlation functional, PBE with D2 dispersion correction and PBE with Tkatchenko and Scheffler (TS) dispersion correction, and searched using ab initio random structure searching. Results show that in general, dispersion-corrected PBE obtained similar lowest minima structures as those obtained via conventional PBE regardless of the type of implementation, although both D2 and TS found several high-energy isomers that conventional PBE did not arrive at, with TS in general giving more structures per energy range that could be attributed to its environment-dependent implementation. Moreover, D2 and TS dispersion corrections found a lowest energy geometry for Li₈ cluster that is in agreement with the structure obtained via the typical benchmarking method diffusion Monte Carlo in a recent work. It is thus suggested that for much larger lithium clusters, utilization of dispersion correction could be of help in searching for lowest energy minima that is in close agreement with that of diffusion Monte Carlo results, but computationally inexpensive.

We present a theoretical study of electronic states and magnetization of two interacting electrons confined in coupled quantum dots (CQDs) presented in a magnetic field. We obtain the eigenenergies of the CQD by solving the relative two-dimensional (2D) Hamiltonian using the combined variational–exact diagonalization method. The dependence of magnetization on temperature, magnetic field strength, confining frequency and barrier height has been investigated. We have shown the singlet–triplet transitions in the ground state of the CQD spectra and the corresponding jumps in the magnetization curves. The comparisons show that our results are in very good agreement with the reported works.

Bunker diesel is an important fuel for heavy duty engines, such as navy ships. It is different from the Ultra Low Sulfur Diesel which is used for highway system vehicles, which has high level sulfur. The Department of Defense (DOD) testified in September 2006 that its energy use represents about 1.2% of total U.S. energy use, of which marine diesel fuel accounts for 13%, that is, 16 million barrels of oil. The Navy spent $900 million for fuel for its ships and aircraft. For fossil-fueled Navy ships, reducing energy use can reduce fuel costs, increase cruising range, increasing its survivability by reducing emissions of hot exhaust gasses. If applied to a significant number of ships, an increase in cruising range might permit a reduction in Navy costs for fuel-related force structure and infrastructure. The flow rate of bunker diesel can be increased 30% by electric field treatment, that is, by reducing the viscosity at least 50%. This could lead to significant cost savings and increase cruising range.

Hydrogen-bonded liquid crystals (HBLCs) have been derived from nonmesogenic citric acid (CA) and mesogenic 4-heptyloxybenzoic acid (7OBA) yielding a highly ordered smectic C (Sm C) phase along with the new smectic X (Sm X) phase which has been identified as fingerprint-type texture. Optical (polarizing optical microscopy), thermal (differential scanning calorimetry) and structural (Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy) properties are studied. A noteworthy observation is that the intermolecular H-bond (between CA and 7OBA) influences on its melting point and clearing temperature of the HBLCs which exhibits lower value than those of the individual compounds. A typical extended mesophase region has been observed in the present complex while varying the mixture ratio (1:1 to 1:3) than those of individual compounds. The change in the ratio of the mesogenic compound in the mixture alters thermal properties such as enthalpy value and thermal span width in nematic (N) region of HBLC complex. Optical tilt angle measurement of CA+7OBA in Sm C phase has been discussed to identify the molecular position in the mesophase.

Recent trends of photovoltaics account for the conversion efficiency limit making them more cost effective. To achieve this we have to leave the golden era of silicon cell and make a path towards III–V compound semiconductor groups to take advantages like bandgap engineering by alloying these compounds. In this work we have used a low bandgap GaSb material and designed a single junction (SJ) cell with a conversion efficiency of 32.98%. SILVACO ATLAS TCAD simulator has been used to simulate the proposed model using both Ray Tracing and Transfer Matrix Method (under 1 sun and 1000 sun of AM1.5G spectrum). A detailed analyses of photogeneration rate, spectral response, potential developed, external quantum efficiency (EQE), internal quantum efficiency (IQE), short-circuit current density (J${}_{\mathrm{\text{SC}}}$), open-circuit voltage (V${}_{\mathrm{\text{OC}}}$), fill factor (FF) and conversion efficiency ($\eta$) are discussed. The obtained results are compared with previously reported SJ solar cell reports.