Numerical proceeding to calculate impurity states in 2D semiconductor heterostructures

The properties of amorphous materials determined by the presence of localized atomic and electronic states are reviewed. Experimental data on atomic dynamics in glasses are described. The two-level-system (TLS) model is presented, and the limits of its applicability analysed. The concept of soft atomic potentials, allowing generalization of the TLS model to higher energies, is introduced. Atomic dynamics in soft potentials, as well as soft-potential coupling with phonons and thermal expansion of glasses, are described. Localized electronic states in glasses are investigated and different theoretical models of such states in glassy semiconductors are reviewed. The connection between localized electronic states and soft potentials is studied. Particular attention is paid to low-relaxation processes in glasses controlled by two-well soft potentials; specifically, low-frequency noise in disordered conductors is considered. The possibility of investigating the localized states in question with the hel...

Within the framework of effective-mass approximation, the properties of the localized electronic states in a N-layer superlattice (SL) with structural defects in finite magnetic fields are investigated by utilizing the transfer matrix and effective barrier-height methods. When the mismatch of electron effective mass in different constituent layers is considered, an external magnetic field will lead to the magneto-coupling. The numerical results show that the magneto-coupling brings about not only quantization of localized electron levels but also the degree of the strong dependence of the localized levels on Landau indices and magnetic fields, especially for the localized levels in higher energy region. In addition, we demonstrate in detail the correlations between the localized electronic states inside the minigaps of the infinite SL with structural defect layer and the resonant transmission peaks in dips of the finite SL. A good coincidence between the localized states and transmission peaks is found, which provides a theoretical basis for experimental observation of the localized electronic states in SLs.

<p indent="0mm">The calculations of neutron-rich lithium isotopes have been performed using the Gamow shell model (GSM). In the present work, the shell model basis is generated by solving the one-body Schrödinger equation of the Woods-Saxon (WS) potential in the complex momentum space. The resulting single-particle basis is composed of bound, resonant and non-resonant continuum states, which is also called the Berggren ensemble. Two-body interaction between nucleons in the Berggren ensemble is derived from the realistic nuclear force CD-Bonn potential with the many-body perturbation theory named the <inline-formula id="INLINE7" content-type="pic"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mover accent="true"><mml:mi other="0">Q</mml:mi><mml:mo other="1" stretchy="true">^</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>-box folded diagrams. The model space consists of the 0p_3/2 bound state, 0p_1/2 resonant state and p_1/2 non-resonant continuum states for neutrons, and 0p_3/2, 0p_1/2 bound states for protons, respectively. The real and imaginary parts of the complex eigenvalues of the shell model Hamiltonian represent the excitation energies and resonance widths of resonant states, respectively. The p-shell neutron-rich lithium isotopes ^7–10Li have been studied. The results of GSM calculations with CD-Bonn potential are compared with traditional shell model with PWT interaction and GSM with surface Gaussian interaction (SGI). The low-lying spectra and resonance widths of resonant states are discussed, as well as the influences of the continuum states on these observables. In terms of the low-lying spectra of well-bound nuclei, the GSM calculations reproduce the excitation energies of ^7–9Li with good accuracy, except for the states with <sc>4 MeV</sc> or higher energies of ⁷Li, which decay through α-particle emission. In the calculation of the unbound nucleus ¹⁰Li, the GSM calculation proves that continuum effect is crucial in its low-lying spectrum. The shell model calculation with PWT interaction of ¹⁰Li overestimates the excitation energies by almost 100%, and by introducing the continuum states, GSM calculation can give more accurate values. Similar phenomenon was also observed in the shell model calculation with USDB interaction of the unbound nucleus ²⁶O, and was explained by the continuum effect as well. As for the resonance widths, the present calculations extend to higher levels of the studied nuclei compared with GSM calculations with the SGI interaction, and obtain reasonable resonance widths of the resonant states. Though the widths of the α-emitting states of ⁷Li cannot be explained by the current GSM, the resonant states among the excited states of ^8–9Li are reproduced in the present work. The GSM calculation with realistic nuclear force also gives correct resonant property of the first 1⁺ state of ¹⁰Li, while the GSM calculation with SGI yields a non-resonant state. The excited state of ¹⁰Li with unknown angular momentum and resonance width is also reproduced, which is predicted to be a 0⁺ state, with <sc>0.13 MeV</sc> width. In the present work, it is proved that the continuum effect is crucial in shell-model calculations of unbound ¹⁰Li. Through treating the continuum effect microscopically, the GSM calculations with properly renormalized realistic nuclear force can reproduce the observed low-lying spectra and resonance widths of both bound and unbound nuclei with high accuracy. On the other hand, the GSM with realistic nuclear force is based on a relatively small model space, and can thus be used to systems with more valence particles. The GSM with realistic nuclear force is proved to be a promising tool for future research on weakly bound or unbound nuclei.

Data have been obtained for the elastic and inelastic scattering of polarized 6Li by 26Mg and 58Ni at energies of 60 MeV and 70.5 MeV, respectively. These data have been compared with the results of coupled‐channels (CC) and continuum‐discretized coupled‐channels (CDCC) calculations performed with interaction potentials generated by the cluster‐folding (CF) technique. CDCC calculations, including couplings to the resonant and nonresonant excited states of 6Li and target excitation, have been found to reproduce data for 6Li+26Mg elastic and inelastic scattering without renormalization of the CF potentials. CC calculations of tensor analyzing powers for the elastic scattering of 6Li by 58Ni are shown to be highly sensitive to the D‐state component of the 6Li ground state wavefunction.

We have studied three characteristics of a hydrogenic impurity located in the center of a quantum pseudodot within the effective mass approximation. These characteristics are the diamagnetic susceptibility, the spin-orbit interaction (SOI), and the relativistic correction (RC). First, we have solved analytically the Shrodinger equation without impurity by using the Laplace transformation. Then, we have applied the variational procedure to obtain energy levels and wave functions with a hydrogenic impurity in the center of quantum pseudodot. According to the results obtained from the present work reveals that (i) the diamagnetic susceptibility increases with increasing the pseudodot size, (ii) The mean value of r 2 increases when the pseudodot size increases, (iii) the SOI and RC increase by increasing the potential V 0, (iv) the RC and SOI approach to zero when the pseudodot increases, (v) the splitting between j=1/2 and 3/2 due to the SOI decreases by increasing pseudodot size.

In the present work, we study three characteristics of a hydrogenic impurity located at the center of a GaAs/Ga1−x Al x As spherical quantum antidot within the effective mass approximation. These characteristics are the diamagnetic susceptibility, the spin-orbit interaction (SOI), and the relativistic correction (RC). First we outline the analytic solution of the corresponding Shrodinger equation with a hydrogenic impurity at the center and obtain the energy levels and wave functions. The results obtained from the present work reveal that the diamagnetic susceptibility increases with increasing the antidot size for finite barrier. The mean value of r 2 increases when the antidot size increases. The SOI and RC increase by increasing the concentration. The RC and SOI approach to zero when the antidot size increases. The splitting between j = 1/2 and 3/2 due to the SOI decreases by increasing antidot size.

The effects of the hydrogenic impurity on the electron-related non-linear optical processes in a InAs/GaAs dome-shaped quantum dot with a wetting layer under applied electric fields are studied within the density-matrix formalism. The one-electron energy levels and wave functions are calculated using the effective mass approximation and the finite element method. The non-linear optical absorption, relative refractive index change and non-linear optical rectification associated with interlevel transitions are calculated under a strong probe field excitation for both in-plane and z-polarisation of the incident light. According to our results as the electric field increases the absorption and dispersion peaks decrease and exhibit red shift. Hydrogenic impurity located at the origin induces a blue shift in the optical responses. For the optical absorption coefficient the peaks magnitude is enhanced by the impurity presence independent of the electric field strengths, whereas the non-linear optical rectification is larger in the case with impurity only for zero applied electric field.

Electronic transition dipoles are crucial for investigating light-matter interactions. Transition dipoles between metastable (autoionizing resonance) states become complex within non-Hermitian formalism, analogous to the resonance energies. Herein, we put forward a robust method for evaluating complex transition dipoles based on real ab initio stabilization calculations. The complex transition dipoles are obtained by analytical continuation via the Padé approximant and are identified as stationary solutions in the complex plane. The capability of the new approach is demonstrated for several transition dipoles of the doubly excited helium resonance states, for which exact values are available for comparison. Nevertheless, the method presented here has no inherent limitation and is suitable for polyatomic systems.

Electromagnetic near-field coupling induced polarization conversion and asymmetric transmission in plasmonic metasurfaces

CDCC calculations of elastic scattering angular distributions for reactions of the weakly bound projectile 6Li with targets 28Si and 58Ni at energies around the Coulomb barrier are presented. Special emphasis is given to account for the effect of couplings from 6Li resonance states l = 2, Jπ = 3+, 2+, 1+. Similarly, the effect produced by non-resonant state couplings is studied. The convergent calculations are carried out with global α-target and d-target interactions. The calculated elastic scattering angular distributions are in general in good agreement with the measurements for the systems considered in this work. It is found that the calculations with only resonance states are very similar to that with all couplings (resonance+non-resonance). So, the absence of these states have a strong effect on elastic scattering (non-resonance states calculation). It is shown that the effects increase as the collision energy increases. An interpretation of the strength of the different effects is given in terms of the polarization potentials that emerge from the different couplings.

Motivated by recent measurements of force detected single-electron tunneling, we present a three-dimensional model for the tunneling rate between a metallic tip and a localized electronic state in a dielectric surface. The tip is assumed to be semi-infinite, with electron wave functions approximated by plane waves. A localized electron state in the dielectric sample is approximated by a spherical quantum well. The tunneling rate is obtained with the help of Bardeen’s approach and is compared with the results for a one-dimensional square barrier model. A comparison with experimental data is also presented.

Deep localized electronic states are created by O2 intercalation into C60 films and C70 films, which causes the Fermi level to shift down to the middle of gap. The states act as a trap level for charge carriers and as nonradiative recombination centers. It seems that prepared C60 films and C70 films have a shallow localized state. The shallow state is located at ∼0.2 eV under the conduction band and affects the electrical and optical properties. Furthermore, the photoirradiation of C60 films and C70 films causes polymerization of the O2-free sample and oxidization of the O2-intercalated sample. The quasistable electronic states at room temperature are created as a result of photo-oxidization of C60 films. C60 oxides create deep localized electronic states which cannot disappear under thermal annealing. The photoluminescence intensity of O2-free samples increases with photoirradiation for 1 h. It is found for the first time that this increase occurs along with a decrease of localized state density.

We show that shot noise can be used for studies of hopping and resonant tunnelling between localised electron states. In hopping via several states, shot noise is seen to be suppressed compared with its classical Poisson value SI = 2eI (I is the average current) and the suppression depends on the distribution of the barriers between the localised states. In resonant tunnelling through a single impurity an enhancement of shot noise is observed. It has been established, both theoretically and experimentally, that a considerable increase of noise occurs due to Coulomb interaction between two resonant tunnelling channels. (© 2003 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Orientation-dependent nonadiabatic molecular high-order-harmonic generation (MHOHG) is studied for the one-electron polar diatomic molecular ion HeH${}^{2+}$ exposed to short, linearly polarized, intense laser fields. The fully dimensional time-dependent Schr\"odinger equation is solved numerically. The resonance of excited states is maximal in the parallel orientation, while it is minimal in the perpendicular case for the nonsymmetric molecular ion. The resulting redshift and the overall intensity of MHOHG strongly depend on the electronic symmetry and charge transfer of the resonant excited states. These results are used to confirm the proposed four-step model in MHOHG involving intermediate resonance states.

Raman spectra obtained in conditions of resonance with electronic excitations are often dominated by transitions that are very weak in the normal off-resonance spectrum. These enhanced bands can be used to determine the symmetry of the resonant excited electronic state if this state gives rise to a forbidden transition. In this case the most strongly enhanced bands correspond to binary combinations and overtones of the vibronic promoting modes active in the transition. The use of this method to determine the symmetry of excited states of butadiene and benzene is presented.1,2 The most strongly enhanced vibrations associated with resonance with allowed electronic transitions are those that have large projections along the geometry change associated with excitation. Recent results for a series of substituted ethylene species are presented. Resonance with excitations that have both allowed and induced vibronic character gives rise to characteristic fundamental transitions of the promoting modes. The case of substituted benzene molecules is discussed.