Electrons in a curvilinear quantum wire

The adiabatic motion of electrons in curvilinear quantum wires was studied. It was assumed that the cross section of a wire was constant along its length. The potential that limited electron motion across a wire and the shape of the cross section of the wire were considered arbitrary, while the curvature and the torsion (defined as the derivative of the cross section rotation angle with respect to the length) were assumed to be small. An effective nonrelativistic Hamiltonian for the motion of electrons along a wire with the conservation of transverse quantum numbers was obtained. The spin-orbit coupling Hamiltonian related to the curvature and torsion of a wire was found. Particular cases of a rectilinear twisted quantum wire with a noncircular cross section and a curvilinear quantum wire on a plane were studied. Various transverse potential models limiting the motion of electrons were considered. In particular, the coefficients of the effective Hamiltonian for quantum wires with rectangular and circular cross sections and hard walls and for wires with a parabolic potential were found.     

Blockade of tunneling in a suspended single-electron transistor

The tunneling of electrons that is limited by the Coulomb blockade effect in a single-electron transistor with a quantum dot based on a narrow GaAs/AlGaAs quantum wire suspended over a substrate is investigated. By means of a direct comparison experiment, the tunneling features associated with the separation of the quantum dot from the substrate are revealed. In addition to an increase in the charge energy (Coulomb gap), which reaches 170 K in temperature units, the dependence of this energy on the number of electrons in the quantum dot, which varies from zero to four, is observed. This dependence is explained by a change in the effective size of the dot due to the effect of the depleting gate voltage. Moreover, the additional blockade of tunneling that is different from the Coulomb blockade and is specific for suspended structures is observed. It is shown that this blockade is not associated with the dynamical effect of exciting local phonon modes and can be attributed to the change in the static elastic strains in the quantum wire that accompany the tunneling of an electron to/from the quantum dot.     

Quantum wire hybridized with a single-level impurity

We have studied low-temperature properties of interacting electrons in a one-dimensional quantum wire (Luttinger liquid) side-hybridized with a single-level impurity. The hybridization induces a backscattering of electrons in the wire which strongly affects its low-energy properties. Using a one-loop renormalization group approach valid for a weak electron-electron interaction, we have calculated a transmission coefficient through the wire, T(epsilon), and a local density of states, nu(epsilon) at low energies epsilon. In particular, we have found that the antiresonance in T(epsilon) has a generalized Breit-Wigner shape with the effective width Gamma(epsilon) which diverges at the Fermi level.     

脉冲放电脱硫反应器中高能电子密度分布的光谱研究

脉冲流光放电产生的大于等于11.2 eV的高能电子能将处于基态的氮分子激发到N₂(C3Π_u)态,测试脉冲流光放电时的N₂(C3Π_u→B3Πg)发射光谱相对强度可以得出脉冲流光放电产生的高能电子的密度。实验在室温常压下研究了空气中线-板式脉冲流光放电脱硫反应器内高能电子密度分布情况,并研究了脉冲电压、反应器的线线间距对反应器内高能电子密度分布的影响。实验结果表明,反应器内的高能电子主要集中在放电线附近高电场区内,随着离放电线的距离增大,高能电子密度减小;脉冲电压对高能电子密度有很大影响,随着电压的升高,高能电子密度基本呈线性增大;线板间距固定,线线间距为线板间距的0.6～1倍时,反应器内高能电子密度分布较为均匀。     

Hot electron temperature and coupling efficiency scaling with prepulse for cone-guided fast ignition

The effect of increasing prepulse energy levels on the energy spectrum and coupling into forward-going electrons is evaluated in a cone-guided fast-ignition relevant geometry using cone-wire targets irradiated with a high intensity (10(20) W/cm(2)) laser pulse. Hot electron temperature and flux are inferred from Kα images and yields using hybrid particle-in-cell simulations. A two-temperature distribution of hot electrons was required to fit the full profile, with the ratio of energy in a higher energy (MeV) component increasing with a larger prepulse. As prepulse energies were increased from 8 mJ to 1 J, overall coupling from laser to all hot electrons entering the wire was found to fall from 8.4% to 2.5% while coupling into only the 1-3 MeV electrons dropped from 0.57% to 0.03%.     

Optical and electronic properties of single modulation doped GaAs/AlGaAs V-grooved quantum wire modified by ion implantation

1 Introduction Recently, there is considerable interest in the fabrication and study of quasi-one di-mensional quantum wires (QWRs) due to their potential application for novel optoelec-tronic devices such as QWR laser array [1,2] etc. Among the various techniques devel-oped for producing quasi-one dimensional (quasi-1D) QWRs, the self-organized growth on patterned substrates has been proven to be one of the most promising methods, due to the simplicity of fabrication[3―5]. The QWR is fa…     

Electron transport across a quantum wire in the presence of electron leakage to a substrate

We investigate electron transport through a mono-atomic wire which is tunnel coupled to two electrodes and also to the underlying substrate. The setup is modeled by a tight-binding Hamiltonian and can be realized with a scanning tunnel microscope (STM). The transmission of the wire is obtained from the corresponding Green’s function. If the wire is scanned by the contacting STM tip, the conductance as a function of the tip position exhibits oscillations which may change significantly upon increasing the number of wire atoms. Our numerical studies reveal that the conductance depends strongly on whether or not the substrate electrons are localized. As a further ubiquitous feature, we observe the formation of charge oscillations.     

Aharonov-Bohm effect in normal metal quantum coherence and transport

We review some of the recent surprising theoretical and experimental results obtained on the transport properties of small disordered metal samples. Even in the presence of disorder, the quantum mechanical interference of electron wavefunctions can still be observed. The Aharonov-Bohm effect is a particularly clear demonstration of this. In doubly connected structures (such as loops of wire) threaded by a magnetic flux, the electrical conductance oscillates because of the Aharonov-Bohm effect. In fact, because the electron trajectories are diffusive (i.e. random walks), even a lone wire (a singly connected structure) will exhibit a random pattern of conductance fluctuations as a function of the magnetic field because of the same interference effects. All that is required for the observation of these interferences is that the electrons retain ‘phase memory’ duing the period of transit through the sample. The length over which memory is maintained (the phase coherence length) can be much larger than the random walk step length (the mean free path). We focus mainly on effects observed in the limit where the phase coherence length of the electrons is comparable to or larger than the sample size. We explain how the interferences are averaged as the system size grows larger than the phase coherence length. We also remark on surprising aspects of the fluctuations such as those resulting from the non-local character of the wavefunction; some of the results are forbidden classically.     

Terahertz acoustic-phonon signal generated by heated electrons in AlGaAs/GaAs-based quantum wires

In this paper, we explore theoretically the possibility of applying AlGaAs/GaAs-based quantum wire systems as a terahertz (THz) ultrasonic generator. For structures such as Al_xGa_1-xAs/GaAs-based low-dimensional semiconductor systems and semiconductor nanostructures, electrons are confined within the nanometer distance scale so that energies (e.g. electronic subband energy, electron kinetic energy, Fermi energy, etc.) are in the meV scale, which consequently results in the acoustic-phonons generated by heated electrons from these novel systems to be around the THz frequency range. Our theoretical results indicate that: (i) Al_xGa_-xAs/GaAs-based quantum wires are suitable for generating THz acoustic-phonon signals; (ii) both longitudinal and transverse acoustic-phonon modes contribute to the detected phonon signals; (iii) the THz ultrasound wave can be generated through both intra- and inter-subband scattering processes; and (iv) the strong dependence of the acoustic-phonon emission from a quantum wire on phonon frequency and phonon emission angle can be observed.     

Quantum thermal conductance of electrons in a one-dimensional wire

We use an electron thermometer to measure the temperature rise of approximately 2 x 10(5) electrons in a two-dimensional box, due to heat flow into the box through a ballistic one-dimensional (1D) constriction. Using a simple model we deduce the thermal conductance kappa(Vg) of the 1D constriction, which we compare to its electrical conductance characteristics; for the first four 1D subbands the heat carried by the electrons passing through the wire is proportional to its electrical conductance G(Vg). In the vicinity of the 0.7 structure this proportionality breaks down, and a plateau at the quantum of thermal conductance pi(2)k(2/B)T/3h is observed.     

Organometallic benzene-vanadium wire: A one-dimensional half-metallic ferromagnet

Using density functional theory we perform theoretical investigations of the electronic properties of a freestanding one-dimensional organometallic vanadium-benzene wire. This system represents the limiting case of multidecker Vn(C6H6)(n+1) clusters which can be synthesized with established methods. We predict that the ground state of the wire is a 100% spin-polarized ferromagnet (half-metal). Its density of states is metallic at the Fermi energy for the minority electrons and shows a semiconductor gap for the majority electrons. We find that the half-metallic behavior is conserved up to 12% longitudinal elongation of the wire. Ab initio electron transport calculations reveal that finite size vanadium-benzene clusters coupled to ferromagnetic Ni or Co electrodes will work as nearly perfect spin filters.     

Intense short-pulse lasers irradiating wire and hollow plasma fibers

When an intense laser pulse irradiates a solid-density foil target, electrons produced at the relativistic critical density can be accelerated to relativistic energy by the ponderomotive force. When a plasma fiber is attached to the back of the foil, the produced relativistic electrons are guided to propagate along the fiber for a long distance, because the high-current electron beam induces strong radial electric fields in the fiber. Transport and heating of intense laser-driven relativistic electrons in both wire and hollow plasma fibers are compared theoretically and numerically. We found that the coupling efficiency from the laser to the plasma fiber depends on the fiber structure. Because of the enhanced return currents in the wire fiber, the temperature in the wire fiber is higher than that in the hollow fiber.     

Theoretical investigation of hot electron cooling process in GaAs/AlAs cylindrical quantum wire under the influence of an intense electromagnetic wave

Hot electrons cooling by phonons in GaAs/AlAs cylindrical quantum wire (CQW), under the influence of an intense electromagnetic wave (EMW), is studied theoretically. Analytic expression for the electron cooling power (CP) is derived from the quantum transport equation for phonons, using the Hamiltonian of interacting electron–optical phonon system. Both photon absorption and emission processes are considered. Numerical results show that the CP reaches maximum when the energy difference between electronic subbands equals the energy of an optical phonon plus the photon energy. Under the influence of the EMW, the negative CP is observed showing that electrons gain energy from phonon and photon instead of losing their energy. Also, the CP increases with increasing the EMW amplitude. Our results theoretically clarify the mechanism of the electron cooling process by phonons in the GaAs/AlAs CQW under the EMW, which is of significance for designing and fabricating high-speed nanoelectronic devices based on this material.     

The Electric Field Outside a Stationary Resistive Wire Carrying a Constant Current

We present the opinion of some authors who believe there is no force between a stationary charge and a stationary resistive wire carrying a constant current. We show that this force is different from zero and present its main components: the force due to the charges induced in the wire by the test charge and a force proportional to the current in the resistive wire. We also discuss briefly a component of the force proportional to the square of the current which should exist according to some models and another component due to the acceleration of the conduction electrons in a curved wire carrying a dc current (centripetal acceleration). Finally, we analyze experiments showing the existence of the electric field proportional to the current in resistive wires.     

Energy partitioning of tunneling currents into Luttinger liquids

Tunneling of electrons of definite chirality into a quantum wire creates counterpropagating excitations, carrying both charge and energy. We find that the partitioning of energy is qualitatively different from that of charge. The partition ratio of energy depends on the excess energy of the tunneling electrons (controlled by the applied bias) and on the interaction strength within the wire (characterized by the Luttinger-liquid parameter κ), while the partitioning of charge is fully determined by κ. Moreover, unlike for charge currents, the partitioning of energy current should manifest itself in dc experiments on wires contacted by conventional (Fermi-liquid) leads.     

Spontaneous formation of a pi soliton in a superconducting wire with an odd number of electrons

We consider a one-dimensional superconducting wire where the total number of electrons can be controlled in the Coulomb blockade regime. We predict that a pi soliton (kink) will spontaneously form in the system when the number of electrons is odd, because this configuration has a lower energy. If the wire with an odd number of electrons is closed in a ring, the phase difference on the two sides of the soliton will generate a supercurrent detectable by a SQUID. The two degenerate states with the current flowing clockwise or counterclockwise can be utilized as a qubit.     

Conductance of short quantum wires with sharp boundaries

The conductance of short ballistic wires with boundaries, whose curvature radius is comparable to the electron wavelength, is investigated. It is found that, in such wires, no conductance quantization takes place. Instead, pronounced interference effects are observed. These effects are related to the Fabry-Perot interference by the wire edges and with the mesoscopic interference caused by the coherent scattering of electrons by the wire edges and by the impurities located in the near-wire regions of the 2D electron gas.     

A nanometric electron multiplexer

A simple nanostructure resonantly coupling two semiconductor quantum wires is proposed as an electron multiplexer, which selectively transfers electrons of a given energy E₀ from one wire to the other, while letting all the neighbouring states within a certain energy range around E₀ propagate virtually unaffected along the input wire. Closed-form expressions are derived for characteristic wire lengths within the coupling structure facilitating such a directional transfer, which enables one to determine optimal parameters for the device fabrication.     

Spin Polarization and Andreev Conductance through a Diluted Magnetic Semiconductor Quantum Wire with Spin--Orbit Interaction

Spin-dependent Andreev reflection and spin polarization through a diluted magnetic semiconductor quantum wire coupled to normal metallic and superconductor electrodes are investigated using scattering theory. When the spin-orbit coupling is considered, more Andreev conductance steps appear at the same Fermi energy. Magnetic semiconductor quantum wire separates the spin-up and spin-down electrons. The Fermi energy, at which different- spin-state electrons begin to separate, becomes lower due to the effect of the spin-orbit interaction. The spin filter effect can be measured more easily by investigating the Andreev conductance than by investigating the normal conductance.     

Photo of a synthetic atom [submillimeter microwave radiationproduction]

Electrons are trapped around thicker sections of selectively etched wire which act as isolated positive nuclei. The trapped electrons are made visible by the glowing clouds around the thicker sections of wire. The object of this work is to improve the performance of an orbitron microwave maser in the production of submillimeter microwave radiation