Narrow Results

Dipole transition moment (DTM) of a hydrogenic donor in a spherical quantum dot of GaAs–Ga_1-xAl_xAs system with finite barrier confinement is obtained. The variational approach within the effective mass approximation is used as the framework for the calculation of donor ionization energy for a few excited states in quantum dot. Calculations of the DTM of an on-center shallow donor hydrogenic impurity in a GaAs quantum dot under hydrostatic pressure are presented. A linear increase in the DTM has been observed, when the dot radius increases from 2 nm to 100 nm. The important conclusions arrived at are (i) ionization energy increases and attains a maximum value occurring for a dot radius of 5 nm, after which the ionization energy decreases gradually as the dot radius increases; (ii) ionization energy for the ground state (1s) is high compared to the excited states (1p and 1d states) and (iii) a linear trend for 1p–1d transition is obtained.

The effects of spin-orbit coupling (SOC) and relativistic correction (RC) on the energy levels of a hydrogenic impurity in a GaAs/Ga_1-xAl_xAs quantum wire are studied. The quantum wire has a V-shaped cross-section and the impurity located in its center. Our numerical calculations have done using a variational procedure within the effective mass approximation. Our results show that (i) the splitting due to the SOC decreases with increasing the wire width, (ii) the SOC and RC increase when the concentration increases, (iii) the SOC is zero for l = 0 (l is angular momentum) and nonzero for l ≠ 0, (iv) for a given wire width, the RC is different for l = 0 and l = 1 due to expectation values of and (r is distance between the electron and impurity). We also computed the conductance of the quantum wire with and without impurity.

The influences of the dispersion, the impurity and the electron–phonon coupling (EPC) on the properties of the Gaussian confining (GC) potential qubit with magnetic field were studied by Pekar-type variation method. Results show that the decoherence time will increase with increasing the dielectric constant (DC) ratio, the dispersion coefficient and the EPC strength, respectively. The phase rotation quality factor increases with increasing the dielectric constant ratio, the dispersion coefficient and EPC strength, respectively. The magnetic field has a regulatory effect on the decoherence time and the phase rotation quality factor.

A method of calculation of donor impurity states in a quantum well is developed. The used techniques have made it possible to find the binding energy both of ground and excited impurity states attached to each QW subband. The positions of the resonant states in 2D continuum are determined as poles of corresponding wave functions. As a result of such an approach the identification of resonant states in 2D continuum is avoided, introducing special criterions. The calculated dependences of binding energies versus impurity position are presented for various widths of Si/Si_1-xGe_x quantum wells.

In this paper, diamond single crystals doped with LiH and boron additives were synthesized in ${\mathrm{\text{Fe}}}_{64}{\mathrm{\text{Ni}}}_{36}$–$\mathrm{\text{C}}$ system under high pressure and high temperature. Under the fixed pressure condition, we found that the synthesis temperature increased slightly after the addition of LiH in the synthesis system. The {100}-orientated surface morphology was investigated by scanning electron microscopy (SEM). The nitrogen concentration in the obtained diamond was analyzed and evaluated using Fourier transmission infrared spectroscopy (FTIR). Furthermore, the electrical properties of Ib-type and boron-doped diamond before and after hydrogenation using Hall effect measurement, which suggested that the conductivity of diamond co-doped with hydrogen and boron was obviously enhanced than that of boron-doped diamond.

Nitrogen (N) is an important impurity in silicon (Si), which associates with impurities as well as with other defects to form defect complexes. The knowledge of the properties and behavior of defect structures containing carbon (C), N and oxygen (O) is important for the Si–based electronic technology. Here, we employ density functional theory (DFT) calculations to investigate the association of nitrogen with carbon and oxygen defects to form the C_iN and C_iNO_i defects. We provide evidence of the formation of these defects and additional details of their structure, their density of states (DOS) and Bader charges. Therefore, C_iN and C_iNO_i defects are now well characterized.

The one-dimensional problem of N particles with contact interaction in the presence of a tunable transmitting and reflecting impurity is investigated along the lines of the coordinate Bethe ansatz. As a result, the system is shown to be exactly solvable by determining the eigenfunctions and the energy spectrum. The latter is given by the solutions of the Bethe ansatz equations which we establish for different boundary conditions in the presence of the impurity. These impurity Bethe equations contain as special cases well-known Bethe equations for systems on the half-line. We briefly study them on their own through the toy-examples of one and two particles. It turns out that the impurity can be tuned to lift degeneracies in the energies and can create bound states when it is sufficiently attractive. The example of an impurity sitting at the center of a box and breaking parity invariance shows that such an impurity can be used to confine a stationary state asymmetrically. This could have interesting applications in condensed matter physics.

In the present work, genetic algorithm method (GA) is applied to the problem of impurity at the center of a spherical quantum dot for infinite confining potential case. For this purpose, any trial variational wave function is considered for the ground state and energy values are calculated. In applying the GA to the problem under investigation, two different approaches were followed. Furthermore, a standard variational procedure is also performed to determine the energy eigenvalues. The results obtained by all methods are found in satisfactory agreement with each other and also with the exact values in literature. But, it is found that the values obtained by genetic algorithm based upon wavefunction optimization are closer to the exact values than standard variational and also than genetic algorithm based on parameter optimization methods.

Scattering of a discrete soliton by a single impurity in dipolar Bose–Einstein condensate is investigated numerically. The results show that the increase of the strength of dipolar interactions leads to repeated reflection, transmission and trapping regions due to energy exchange between the center of mass motion and the internal modes of the impurity. However, increasing the strength of the attractive nonlocal dipole–dipole interaction will result in different scattering windows. While the dipole–dipole interaction can significantly expand the trapping region of the system, nevertheless transmission resonances through the impurity are still observed.

In this paper, the effect of dilute charged impurity and external magnetic field on orbital-resolved density of states (DOS) and electronic heat capacity (EHC) of a monolayer hydrogenated graphene which is called chair-like graphane is investigated within the Harrison model and Green’s function technique. The self-consistent Born approximation has been implemented to describe the effect of scattering between electrons and dilute charged impurities. Our results show that the graphane is a semiconductor and its band gap decreases with impurity and magnetic field. EHC reaches almost linearly to Schottky anomaly and does not change at low temperatures in the presence of impurity and magnetic field. Generally, EHC increases with the mentioned parameters. Surprisingly, impurity doping only affects the salient behavior of $p_y$ orbital contribution of carbon atoms due to the symmetry breaking.

In this work, the influence of boron atom impurity is investigated on the electronic properties of a single-wall carbon nanotube superlattice which is connected by pentagon–heptagon topological defects along the circumference of the heterojunction of these superlattices. Our calculation is based on tight-binding $\pi$-electron method in nearest-neighbor approximation. The density of states (DOS) and electronic band structure in presence of boron impurity has been calculated. Results show that when boron atom impurity and nanotube atomic layers have increased, electronic band structure and the DOS have significant changes around the Fermi level.

We have investigated the effect of impurity X (X = C and O) atoms on the behavior of hydrogen in vanadium, which is an ideal structural material for nuclear fusion reactors, by first-principles calculations. We found that (1) in bulk V, the interaction between an interstitial H atom and an X atom is repulsive, and the interaction with O is much stronger than that with C. (2) The X–vacancy (vac) cluster can act as a center for capturing H in V. The C-vac cluster can trap as many as two H atoms, while the O–vac cluster can capture up to four H atoms. (3) C and O impurities can effectively decrease the trapping energy of a single H atom in a vacancy. The H-trapping energies in the C–vac and O–vac complexes are 0.88 eV and 0.46 eV, respectively, both of which are lower than those in the X-free vacancy. (4) Both H–X and X-metal interactions affect the H solubility in V. The above results provide important information for application of vanadium as a structural material for nuclear fusion tokamaks.

The optimal usage of designed fuel pellets is one of the very important parameters in inertial confinement fusion (ICF) systems. In this research, time-dependent dynamical equations for D/D fuel are written by considering impurity of ⁶Li. Then dependency of gain on temperature, density and pellet radius is studied using Runge–Kutta method. The obtained results show that the energy gain will be maximized at the initial temperature 35 keV, density, 5000 g/cm³ and ratio impurity of ⁶Li, 0.05.