Quantum effects of potential fluctuations in GaAs δ-doping superlattices

The electronic and optical properties of δ-doping n-i-p-i superlattices are strongly influenced by the random distribution of donors and acceptors within the doping layers. A Monte-Carlo method is applied to investigate the resulting potential fluctuations and local changes of energy levels and wavefunctions. We study disorder effects on the density of states, the capacitance and the intraband absorption coefficient as a function of excitation level. In addition, the luminescence spectra are calculated and compared to electroluminescence measurements. Excellent agreement is achieved without using any fitting parameters, if the local wavefunction shrinkage of the tail states is included. While contributions of different subbands cannot be resolved in the luminescence, the simulation of conduction band (CB) intraband absorption confirms that this is possible using resonant Raman scattering.     

The effect of nonlinearity in relativistic nucleon–nucleon potential

A simple form for nucleon–nucleon (NN) potential is introduced as an alternative to the popular M3Y form using the relativistic mean field theory (RMFT) with the non-linear terms in σ-meson for the first time. In contrast to the M3Y form, the new interaction becomes exactly zero at a finite distance and the expressions are analogous with the M3Y terms. Further, its applicability is examined by the study of proton and cluster radioactivity by folding it with the RMFT-densities of the cluster and daughter nuclei to obtain the optical potential in the region of proton-rich nuclides just above the double magic core¹⁰⁰Sn. The results obtained were found comparable with the widely used M3Y NN interactions.     

The intermolecular potential energy surface of Ar · HC1

Anisotropic potential energy surfaces for Ar · HC1 are obtained by simultaneous least squares fitting to molecular beam spectra, rotational line broadening cross sections, second virial coefficients and molecular beam total differential cross sections. Several potentials are obtained which given good agreement with all these data and the sensitivity of the data to various aspects of the potential is investigated. For all potentials the equilibrium configuration is linear with the atomic arrangement Ar · H-C1. Several different ways of parameterizing the intermolecular potential are considered and it is concluded that the conventional multipole parameterization is not adequate for strongly anisotropic intermolecular potentials.     

Observations of structural deviations in MBE grown II–VI superlattices

X-ray diffraction analyses of HgTeCdTe and CdTeZnTe superlattices (SL's) have revealed a few exceptional samples possessing complex satellite structures that cannot be attributed to a single modulation period of one specific average composition. All of the examined SL's were grown, by molecular beam epitaxy (MBE), to have one well-defined period. Four of these unique SL's are reviewed and the observed deviations with respect to a single period SL model are illustrated.The SL samples are characterized by several diffraction techniques. Extended x-ray ω − 2θ scans were performed with the scattering vector along the SL growth direction. These scans were complemented by ω scans to assess the lateral coherence of the diffracting planes.The complex diffraction spectra suggest that several SL regions coexist within one macroscopic sample. Differences in the period and average composition distinguish each domain by observing the satellite spacing and central peak position, respectively.     

The wake potential in the viscous quark–gluon plasma

Based on the dielectric function derived from the viscous chromohydrodynamic approach, we investigate the wake potential induced by a fast parton traveling through the viscous quark–gluon plasma. An oscillatory wake potential and a Lennard-Jones potential are found in the backward direction for the fast parton speeds v=0.99c$v=0.99c$ and v=0.55c$v=0.55c$, respectively. In the forward direction, there is a modified Coulomb screening potential for both two speeds. When v=0.99c$v=0.99c$, shear viscosity makes the oscillation of potential more remarkable with the increase of η/s$\eta /s$. While v=0.55c$v=0.55c$, the viscous effects on the wake potential are very trivial in both the forward and backward directions. Finally, we give some explanations for the speed-dependent viscous effects on the wake properties.     

Relation between quantum NOT gate speed and asymmetry of the potential of RF-SQUID

This paper investigates the relationship between the speed of a quantum not gate and the asymmetry of the potential in an interactive system formed by a two-level RF-SQUID qubit and a classical microwave pulse. The RFSQUID is characterized by an asymmetric double well potential which gives rise to diagonal matrix elements that describe the interaction of the SQUID with the microwave pulse. And the diagonal matrix elements account for the interaction of the microwave pulse with the SQUID. The results indicate that, when the angular frequency of the microwave field is chosen as near resonate with the transition （0） ←→ （1）, i.e. ω1 -ω0 ≈ ωm, （1） the gate speed is decided by three factors, the Rabi frequency, the difference of the diagonal matrix elements between the two levels, and the angular frequency of the applied microwave pulse ωm; （2） the gate speed descends when the asymmetry of the potential is considered.     

Classical theory of atom–surface scattering: The rainbow effect

The scattering of heavy atoms and molecules from surfaces is oftentimes dominated by classical mechanics. A large body of experiments have gathered data on the angular distributions of the scattered species, their energy loss distribution, sticking probability, dependence on surface temperature and more. For many years these phenomena have been considered theoretically in the framework of the “washboard model” in which the interaction of the incident particle with the surface is described in terms of hard wall potentials. Although this class of models has helped in elucidating some of the features it left open many questions such as: true potentials are clearly not hard wall potentials, it does not provide a realistic framework for phonon scattering, and it cannot explain the incident angle and incident energy dependence of rainbow scattering, nor can it provide a consistent theory for sticking. In recent years we have been developing a classical perturbation theory approach which has provided new insight into the dynamics of atom–surface scattering. The theory includes both surface corrugation as well as interaction with surface phonons in terms of harmonic baths which are linearly coupled to the system coordinates. This model has been successful in elucidating many new features of rainbow scattering in terms of frictions and bath fluctuations or noise. It has also given new insight into the origins of asymmetry in atomic scattering from surfaces. New phenomena deduced from the theory include friction induced rainbows, energy loss rainbows, a theory of super-rainbows, and more. In this review we present the classical theory of atom–surface scattering as well as extensions and implications for semiclassical scattering and the further development of a quantum theory of surface scattering. Special emphasis is given to the inversion of scattering data into information on the particle–surface interactions.     

An investigation of the gate dependence in an electronic Aharonov–Bohm interferometer

In this study we have obtained the dependence of the electronic distribution on the gate shape and the applied gate voltage in a quantum Hall effect based Aharonov–Bohm interferometer using a method presented in our previous studies. We have discussed the relation between the distribution of incompressible strips and observation of Aharonov–Bohm oscillations. We have obtained the distributions of the incompressible strips for various gate voltages and have shown that a gate potential sweep and a magnetic field sweep would be equivalent. Our calculations also predict that for wider gate separations it is possible observe a silent region while sweeping the magnetic field or the gate voltage.     

An alternative method for the exact calculation of Wannier–Stark localization in superlattices

We present an alternative method for the exact calculations of the Wannier–Stark (WS) localization in a long periodic potential corresponding to a (50 Å/30 Å) GaAs/Ga_0.7Al_0.3As superlattice. We show that the electric field dependence of the electron wavefunction has unique localization dynamics. One interesting prediction is a small effect involving the change of the dipole field with increasing WS field. It is argued that this may give rise to parasitic effects in Bloch oscillations and, therefore, to noise in coherent terahertz emission.     

Implementation of all-optical Toffoli gate in Λ-systems

An optical Toffoli gate is the essential logical element, which permits the implementation of a reversible optical processor. We propose a simple realization of such a gate in films of crystals doped with rare-earth ions. The proposed scheme is based on adiabatic population transfer in a ??-system by means of counterintuitive and intuitive sequences of short laser pulses. We also discuss possibilities for experimental realization of the proposed gate.     

Fano-like electron–phonon interference in δ-doping GaAs superlattices

The interaction between electron excitations and LO phonons is studied by Raman scattering inδ-doping GaAs superlattices. The Raman spectra measured close to the E₀ +  Δ₀resonance of GaAs present Fano-like coupling of the LO phonons with the quasicontinuum single-particle electron excitations. Due to the self-consistent origin of the electron-energy spectrum in δ-doping superlattices the resonance of the Fano interference was found to be strongly dependent on the electron density as well as the excitation energy.     

The interplay of single-particle and collective motions in the low-lying states of ■ with quadrupole-octupole correlations

The beyond mean-field approach for low-lying hypernuclear states is extended by mixing the confgurations associated with both single-particle and quadrupole-octupole collective excitations within the generator coordinate method based on a covariant density functional theory. The method is demonstrated in the application to the low-lying states of ²¹_ΛNe, where the confgurations with the Λ hyperon occupying the frst(Λ_s) and second(Λ_p) lowest-energy state...     

Dynamic dc voltage band in vertical transport of superlattices

By the numerical method, we show a transition process from static to dynamic electric-field domain formation in semiconductor superlattices. During this transition, there can be noticed a sawtooth-like zone in which static and dynamic electric-field domain zones appear alternatively with increasing voltage. Therefore, a dynamic dc voltage band emerges from each sawtooth-like branch of the current－voltage characteristic. These results are qualitatively in agreement with experiment.     

Ab initio potential energy surface and intermolecular vibrational frequencies of C3–Ar complex

The intermolecular potential energy surfaces for C₃–Ar have been calculated by supermolecular CCSD(T) and MP4 methods. The MP4 and CCSD(T) potentials have similar global behaviours. Their global minima all correspond to the slightly distorted T-shaped geometries. From these two potentials, the intermolecular vibrational energies and wavefunctions were calculated. The energy level patterns of the vdW vibrational states were predicted for the C₃–Ar complex. The zero point bending motion of this complex has a range of approximately 60°. The calculated transition frequencies of vdW bending agree well with available experimental data.     

Modeling of ionization–recombination processes in the atmospheric surface layer

The electrical structure of non-stationary horizontally-homogenous surface layer with multi-charged aerosol particles was mathematically modeled in the approximation of turbulent electrode effect. The profiles of positive and negative small ions and nuclei, electric field, polar air conductivity, current density and space charge density were computed in different time periods and various physical conditions. The mathematical model of non-stationary horizontally homogenous surface layer with aerosol particles was made regarding turbulent mixing and convective transport. The space-time distributions of positive and negative small ions and nuclei, electric field, electrical conductivity, current density and space charge density for various physical conditions (aerosol concentrations, turbulent mixing, convective transport, air ionization rate, electric field strength near surface, aerosol particles size) were received. Experimental data of electrical and meteorological parameters were measured and analyzed. It was received that theoretical results are in a good agreement with experimental data.     

Resonant peak splitting through magnetic Kronig–Penney superlattices in graphene

The resonance splitting effect of Dirac electrons through magnetic Kronig–Penney superlattices with delta-function barriers in graphene is studied theoretically. It is found that both transmission probability and conductance present (n−1)-fold$(n-1)\mathrm{-}\mathrm{fold}$ resonant peak splitting in n vector potential barriers, which is the same as that of standard electrons in semiconductor superlattices [R. Tsu, L. Esaki, Appl. Phys. Lett. 22 (1973) 562]. The resonant peak splitting and wave-vector filtering could be controlled by adjusting the transverse wave vector and structural parameters. These properties may be useful for the design of graphene-based electronic devices.     

Temperature dependence in atom–surface scattering

It is shown that a straightforward measure of the temperature dependence of energy resolved atom–surface scattering spectra measured under classical conditions can be related to the strength of the surface corrugation. Using classical perturbation theory combined with a Langevin bath formalism for describing energy transfer, explicit expressions for the scattering probabilities are obtained for both two-dimensional, in-plane scattering and full three-dimensional scattering. For strong surface corrugations results expressed as analytic closed-form equations for the scattering probability are derived which demonstrate that the temperature dependence of the scattering probability weakens with increasing corrugation strength. The relationship to the inelastic rainbow is briefly discussed.     

Acoustic waves in (001) InN–AlN and InN–GaN superlattices

We study the acoustic waves of (001) InN–AlN and InN–GaN superlattices. We obtain the dispersion curves for various symmetric and general orientations of the wavevector parallel to the interfaces. The results reveal the impact of the elastic anisotropy due to the zinc-blende structure of the constituent materials. It is found that for certain material parameters and orientations, the dispersion curves exhibit wide gaps with potential for the existence of surface localized waves.