Coherent tunnelling in coupled quantum wells under a uniform magnetic fields

Coherent tunnelling is studied in framework of the effective mass approximation for an asymmetric coupled quantum well. The Hartree potential due to the electron-electron interaction is considered in our calculation. The effects of the longitudinal and transverse magnetic field on coherent tunnelling characteristics are discussed. It has been found that the external field plays an important role in modulating the electron states.

The influence of internal electric fields on the transition energy of InGaN/gaN quantum well

We present a new way to meet the amount of strain relaxation in an InGaN quantum well layer grown on relaxed GaN by calculating and measuring its internal field. With perturbation theory, we also calculate the transition energy of InGaN/GaN SQWs as affected by internal fields. The newly reported experimental data by Graham et al. fit our calculations well on the assumption that the InGaN well layer suffered a 20% strain relaxation, we discuss the differences between our calculated results and the experimental data. Our calculation suggests that with the increase of indium mole fraction in the InGaN/GaN quantum well, the effect of polarization fields on the luminescence of the quantum well will increase. Moreover, our calculation also suggests that an increase in the quantum well width by only one monolayer can result in a large reduction in the transition energy. (c) 2006 Elsevier B.V. All rights reserved.

Hole Rashba effect and g-factor in InP nanowires

The hole Rashba effect and g-factor in InP nanowires in the presence of electric and magnetic fields which bring spin splitting are investigated theoretically in the framework of eight-band effective-mass envelop function theory, by expanding the lateral wave function in Bessel functions. It is well known that the electron Rashba coefficient increases nearly linearly with the electric field. As the Rashba spin splitting is zero at zero k(z) ( the wave vector along the wire direction), the electron g-factor at k(z) = 0 changes little with the electric field. While we find that as the electric field increases, the hole Rashba coefficient increases at first, then decreases. It is noticed that the hole Rashba coefficient is zero at a critical electric field. The hole g-factor at k(z) = 0 changes obviously with the electric field.

Rashba spin-orbit coupling in InSb nanowires under transverse electric field

We investigate the Rashba spin-orbit coupling brought by transverse electric field in InSb nanowires. In small k(z) (k(z) is the wave vector along the wire direction) range, the Rashba spin-orbit splitting energy has a linear relationship with k(z), so we can define a Rashba coefficient similarly to the quantum well case. We deduce some empirical formulas of the spin-orbit splitting energy and Rashba coefficient, and compare them with the effective-mass calculating results. It is interesting to find that the Rashba spin-orbit splitting energy decreases as k(z) increases when k(z) is large due to the k(z)-quadratic term in the band energy. The Rashba coefficient increases with increasing electric field, and shows a saturating trend when the electric field is large. As the radius increases, the Rashba coefficient increases at first, then decreases. The effects of magnetic fields along different directions are discussed. The case where the magnetic field is along the wire direction or the electric field direction are similar. The spin state in an energy band changes smoothly as k(z) changes. The case where the magnetic field is perpendicular to the wire direction and the electric field direction is quite different from the above two cases, the k(z)-positive and negative parts of the energy bands are not symmetrical, and the energy bands with different spins cross at a k(z)-nonzero point, where the spin splitting energy and the effective g factor are zero.

Spin-polarized transport in one-dimensional waveguide structures with spatially periodic electric fields

We investigate theoretically spin-polarized transport in a one-dimensional waveguide structure under spatially periodic electric fields. Strong spin-polarized current can be obtained by tuning the external electric fields. It is interesting to find that the spin-dependent transmissions exhibit gaps at various electron momenta and/or gate lengths, and the gap width increases with increasing the strength of the Rashba effect. The strong spin-polarized current arises from the different transmission gaps of the spin-up and spin-down electrons. (c) 2006 American Institute of Physics.

Spin-polarized transport in one-dimensional waveguide structures with spatially-periodic electronic and magnetic fields

We investigate theoretically the spin-polarized transport in one-dimensional waveguide structure with spatially-periodic electronic and magnetic fields. The interplay of the spin-orbit interaction and in-plane magnetic field significantly modifies the spin-dependent transmission and the spin polarization. The in-plane magnetic fields increase the strength of the Rashba spin-orbit coupling effect for the electric fields along y axis and decrease this effect for reversing the electric fields, even counteract the Rashba spin-orbit coupling effect. It is very interesting to find that we may deduce the strength of the Rashba effect through this phenomenon. (c) 2005 Elsevier Ltd. All rights reserved.

A new development on ANN in China - Biomimetic pattern recognition and multi weight vector neurons

A new model of pattern recognition principles-Biomimetic Pattern Recognition, which is based on "matter cognition" instead of "matter classification", has been proposed. As a important means realizing Biomimetic Pattern Recognition, the mathematical model and analyzing method of ANN get breakthrough: a novel all-purpose mathematical model has been advanced, which can simulate all kinds of neuron architecture, including RBF and BP models. As the same time this model has been realized using hardware; the high-dimension space geometry method, a new means to analyzing ANN, has been researched.

Collective and single-particle excitations in coupled quantum wires in magnetic fields

The full spectra of magnetoplasmons and single-particle excitations are obtained of coupled one-dimensional electron gases in parallel semiconductor quantum wires with tunneling. We show the effects of the interwire Coulomb interaction and the tunneling, as well as the magnetic-field-induced localization on the elementary excitations in symmetric and asymmetric coulped quantum wire structures. The interacton and resonance between the plasmon and the intersubband single-particle excitations are found in magnetic fields.

Strong three-level resonant magnetopolaron effect due to the intersubband coupling in heavily modulation-doped GaAs/AlxGa1-xAs single quantum wells at high magnetic-fields

Electron cyclotron resonance CR) measurements have been carried out in magnetic fields up to 32 T to study electron-phonon interaction in two heavily modulation-delta -doped GaAs/Al0.3Ga0.7As single-quantum-well samples. No measurable resonant magnetopolaron effects were observed in either sample in the region of the GaAs longitudinal optical (LO) phonons. However, when the CR frequency is above LO phonon frequency, omega (LO)=E-LO/(h) over bar, at high magnetic fields (B>27 T), electron CR exhibits a strong avoided-level-crossing splitting for both samples at frequencies close to (omega (LO)+ (E-2-E-1)1 (h) over bar, where E-2, and E-1 are the energies of the bottoms of the second and the first subbands, respectively. The energy separation between the two branches is large with the minimum separation of 40 cm(-1) occurring at around 30.5 T. A detailed theoretical analysis, which includes a self-consistent calculation of the band structure and the effects of electron-phonon interaction on the CR, shows that this type of splitting is due to a three-level resonance between the second Landau level of the first electron subband and the lowest Landau level of the second subband plus one GaAs LO phonon. The absence of occupation effects in the final states and weak screening or this three-level process yields large energy separation even in the presence of high electron densities. Excellent agreement between the theory and the experimental results is obtained.

Strong resonant intersubband magnetopolaron effect in heavily modulation-doped GaAs/AlGaAs single quantum wells at high magnetic fields

Electron cyclotron resonance (CR) has been studied in magnetic fields up to 32 T in two heavily modulation-delta-doped GaAs/Al0.3Ga0.7As single quantum well samples. Little effect on electron CR is observed in either sample in the region of resonance with the GaAs LO phonons. However, above the LO-phonon frequency energy E-LO at B > 27 T, electron CR exhibits a strong avoided-level-crossing splitting for both samples at energies close to E-LO + (E-2 - E-1), where E-2, and E-1 are the energies of the bottoms of the second and the first subbands, respectively. The energy separation between the two branches is large, reaching a minimum of about 40 cm(-1) around 30.5 T for both samples. This splitting is due to a three-level resonance between the second LI, of the first electron subband and the lowest LL of the second subband plus an LO phonon. The large splitting in the presence: of high electron densities is due to the absence of occupation (Pauli-principle) effects in the final states and weak screening for this three-level process. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Electronic states of InAs verfically-assembled quantum disks in magnetic fields and two-electron quantum-disk qubit

We have studied the single-electron and two-electron vertically-assembled quantum disks in an axial magnetic field using the effective mass approximation. The electron interaction is treated accurately by the direct diagonalization of the Hamiltonian matrix. We calculate the six criergy levels of single-electron quantum disks and the two lowest energy levels of two-electron quantum disks in an axial magnetic field. The change of the magnetic field as an effective potential strongly modifies the electronic structures. leading to splittings and crossings between levels The results demonstrate the switching between the around states with the total spins S = 0 and S = 1. The switching results in a qubit allowed to fabricate by current growth techniques.

Performance of an embedded optical vector matrix multiplication processor architecture

An embedded architecture of optical vector matrix multiplier (OVMM) is presented. The embedded architecture is aimed at optimising the data flow of vector matrix multiplier (VMM) to promote its performance. Data dependence is discussed when the OVMM is connected to a cluster system. A simulator is built to analyse the performance according to the architecture. According to the simulation, Amdahl's law is used to analyse the hybrid opto-electronic system. It is found that the electronic part and its interaction with optical part form the bottleneck of system.

on a class of pseudorandom sequences from elliptic curves over finite fields

Following the idea of Xing et al., we investigate a general method for constructing families of pseudorandom sequences with low correlation and large linear complexity from elliptic curves over finite fields in this correspondence. With the help of the tool of exponential sums on elliptic curves, we study their periods, linear complexities, linear complexity profiles, distributions of r-patterns, periodic correlation, partial period distributions, and aperiodic correlation in detail. The results show that they have nice randomness.