Narrow Results

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.

We examine some new DNLS-like equations that arise when considering strongly-coupled electron-vibration systems, where the local oscillator potential is anharmonic. In particular, we focus on a single, rather general nonlinear vibrational impurity and determine its bound state(s) and its dynamical selftrapping properties.

A first-order differential equation of Green's function, at the origin G(0), for the one-dimensional lattice is derived by simple recurrence relation. Green's function at site (m) is then calculated in terms of G(0). A simple recurrence relation connecting the lattice Green's function at the site (m, n) and the first derivative of the lattice Green's function at the site (m ± 1, n) is presented for the two-dimensional lattice, a differential equation of second order in G(0, 0) is obtained. By making use of the latter recurrence relation, lattice Green's function at an arbitrary site is obtained in closed form. Finally, the phase shift and scattering cross-section are evaluated analytically and numerically for one- and two-impurities.

By using the concept of concurrence, we study pairwise entanglement between the two end spins in the open-ended Heisenberg XXX and XY chains up to ten spins. The results show that by introducing two boundary impurities, one can obtain maximum entanglement at the limit of the impurity parameter |J₁| ≪ J for the even-number qubits. When |J₁/J| > 0, the entanglement always decreases with the increase in the absolute value of J₁/J, and for the Heisenberg XXX chain, C disappears when J₁/J exceeds a certain critical point J_ic, and attains an asymptotic value C₀ when |J₁| ≫ J(J₁ < 0), while for the Heisenberg XY chain, C always disappears when |J₁/J| exceeds a certain critical point J_ic. Both C₀ and J_ic decrease with the increase of the length of the chain.

The ground-state exciton binding energy and interband emission wavelength in the direct-gap Ge/SiGe quantum dot (QD) are investigated by means of a variational approach, within the framework of effective-mass approximation. Numerical results show that the ground-state exciton binding energy has a maximum value with increasing quantum size of the direct-gap Ge/SiGe QD. The interband emission wavelength is increased when the QD size is increased. Our results indicate the direct-gap Ge/SiGe QD can be applied for long wavelength optoelectronic devices.

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.

Based on the effective-mass approximation, the acceptor binding energy in a cylindrical zinc-blende (ZB) InGaN/GaN single quantum dot (QD) is investigated variationally in the presence of the applied electric field. Numerical results show that the acceptor binding energy is highly dependent on the applied electric field, impurity positions and QD size. The applied electric field also induces an asymmetric distribution of the acceptor binding energy with respect to the center of the QD. Moreover, in the presence of the applied electric field, the acceptor binding energy is insensitive to dot height when the impurity is located at the left boundary of the ZB In_0.1Ga_0.9N/GaN QD with large dot height (H≥6 nm). In particular, the acceptor binding energy of the impurity located at the left boundary of the ZB In_0.1Ga_0.9N/GaN QD is identical for different dot height when the applied electric field F≥350 KV/cm. This result can be of interest for the technological purpose, as it could involve a source of control some impurity-related properties in these systems under the applied electric field.

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.

The electron paramagnetic resonance (EPR) $g$ factor formulas for Cr${}^{5+}$ and V${}^{4+}$ ions in Al₂O₃, TiO₂ and VO₂ crystals are deduced from Jahn–Teller effect and contributions of the charge transfer (CT) levels. The tetragonal distortions. $\mathrm{\Delta }R(R_{\parallel }-R_{\perp })=-0.0184,-0.0045$ and −0.0124 nm, and $\mathrm{\Delta }𝜃=0^{\circ }$, $-0.001^{\circ }$ and 0${}^{\circ }$, for Al₂O₃:Cr${}^{5+}$, TiO₂:V${}^{4+}$ and VO₂, respectively. The calculations of the $g$ factors agree well with the experimental values. The contributions of the CT levels to $g$ factors increase with the increasing valence state. It must be taken into account in the precise calculations of $g$ factors for the high valence state $d^1$ ions in crystals.

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.

In this work, we consider the results of studying the spectral distribution, the temperature dependence of photoconductivity, and the dependence of the spectral distribution of photoconductivity on the applied electric field of doped with rare earth elements GaTe single crystals in the temperature range of 30–300 K. As the temperature decreases to 30 K, the impurity peaks disappear, and the intense maximum shifts to the short wavelength region. The increase in impurity photoconductivity with increasing temperature is due to the thermooptical filling of acceptor levels with electrons and their further transition to the conduction band under the action of illumination. Such a temperature dependence of the photoconductivity is explained by the presence of acceptor levels in the band gap.