We constructed the Hamiltonian of spin–orbit splitting for carriers of a tubular electron gas in InAs nanowires. The spectral problem is solved using an exact numerical diagonalization. It is shown that the contribution of k-linear Dresselhaus-like spin–orbit (SO) coupling leads to renormalization of the so-called SO-gaps and appearance of anticrossings in subband spectrum. These features can be detected in ballistic transport. 相似文献
We investigate the electron transmission through a structure of
serial mesoscopic metallic rings coupled to two external leads. A
set of analytical expressions based on the quantum waveguide
transport and the transfer matrix method are derived and used to
discuss the effects of geometric configurations on transmission
probabilities. It is found that in the contact ring case the
existence of an applied magnetic flux is necessary to create
transmission gaps, while in the non-contact ring case transmission
gaps always appear irrespective of whether there is an applied
magnetic flux or not. The transmissions for periodic rings with a
defect ring and periodic rings built by two sorts of rings are
also briefly studied. It is also found that the transmission
periodicity with wave vector must be ensured by the
commensurability of two characteristic lengths, i.e., of the half
perimeter of a ring and the connecting wire between two adjacent
rings. The special points of wave vector and magnetic flux which
give rise to the transmission resonance and antiresonance are
analyzed in detail. 相似文献
A new method is proposed to realize a constant charge operation in a size effect modulation LED (SEM/LED) with a high speed switching capability. The theoretical estimation shows a possibility of promising LED mode operation of the SEM/LED at 300K with the aid of the proposed circuit scheme. 相似文献
Investigation of the photoelectric yield characteristics of the negative electron affinity NEA (100) diamond surface (produced by hydrogen plasma exposure) finds a striking similarity to the emission from NEA (111) diamond surfaces. Work on NEA diamond (111) surfaces has revealed the important role (sometimes dominant) of photoexcited excitons in the photoelectric yield. Comparison of the electron emission properties among surfaces with different crystallographic orientations can give further insight into electron emission mechanisms. We find that the kinetic energy distribution, the photon energy dependence of photoelectric yield, and the photon energy dependence of constant final state measurements of NEA (100) diamond are characteristically similar to the emission from NEA (111) diamond surfaces. Observed differences appear related to the change in band bending at the surface. 相似文献
A long‐standing debate in the theory of hopping insulators concerns the role of multi‐electron transitions in the dynamics of the system. The natural assumption is that as temperature is lowered, two‐electron transitions will play an increasingly important role since they provide a way of tunneling through additional energy barriers which would be energetically unfavorable as successive one‐electron transitions. This was disputed in [1], but later it was seen in [2]. The reason for this discrepancy is not clear and deserves further attention. One point where the two approaches diverged was in the selection and weighting of the two‐electron transitions relative to one‐electron transitions. We present calculations of the transition rates to second order in the tunneling matrix element, which will be used in improved numerical studies. We compare results for only one‐electron jumps with results including also two‐electron jumps. 相似文献
This paper describes the results of irradiation of specimens of copper and copper containing up to 2 at % beryllium in the high-voltage electron microscope. The results of irradiation at temperatures ranging from 20–500 K are described and discussed in the light of recently proposed theories of defect nucleation. Although the results are difficult to interpret because of the many diverse factors which influence the nucleation and growth of the damage it was found that the values for the volume density of defects were in general agreement with the predictions, if the effects of the foil surfaces were taken into account. The corrected densities were used to derive values for the activation energy for motion of an interstitial in copper, Em, and the binding energy between an interstitial and a beryllium atom, Eb. The results obtained were 0.12±0.03 eV for Em and 0.29±0.07 eV for Eb. 相似文献
We report room temperature (20 °C) continuous-wave operation of 1.55 μm vertical-external-cavity surface-emitting lasers. The optically pumped monolithic InP-based structure, grown by metal–organic chemical vapor deposition, includes a InP/InGaAsP Bragg reflector, and an active region with strain compensated quantum wells. Output power up to 4 mW is obtained at 0 °C. The thermal impedance of the structure is deduced from the experimental data. 相似文献
A new type of phase transition has been found in the two-dimensional XY-model using Monte Carlo simulations, which show a divergence of susceptibility, but no divergence of specific heat. Vortices appear below Tc as was predicted by Kosterlitz and Thouless. 相似文献
We have characterized the properties of three AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor structures with two different well widths fabricated by molecular beam epitaxy on (0 0 1) GaAs substrates with different threading dislocation densities using room temperature photoreflectance (PR) and photoluminescence (PL). The samples were denoted as A, B and C with well widths of 140, 160 and 160 Å, respectively. Samples A and B were grown on substrates with lower threading dislocation densities. For samples B and C, the well width exceeds the pseudomorphic limit so that there is some strain relaxation and related misfit dislocations, as determined from X-ray measurements. In order to detect the anisotropic strain of the misfit dislocations related to strain relaxation, the PR measurements were performed for incident light polarized along [1 1 0] and
directions. Evidence for the influence of the strain relaxation upon the relaxed channel was provided by the observed anisotropy of the polarized PR features and reduction of the intensity of PL signals in the InGaAs channel layer. The lowest lying intersubband transition has been confirmed by a comparison of the PR and PL spectra. Signals have been observed from every region of the sample making it possible to evaluate the In and Al compositions, channel width and two-dimensional electron gas density as well as the properties of the GaAs/AlGaAs multiple quantum well buffer layer. 相似文献
Ultrasonic irradiation (22 kHz, Ar atmosphere) of Th(IV) β-diketonates Th(HFAA)4 and Th(DBM)4, where HFAA and DBM are hexafluoroacetylacetone and dibenzoylmethane respectively, causes them to decompose in hexadecane solutions, forming solid thorium compounds. The first-order rate constants for Th(IV) β-diketonate degradation were found to be (9.3±0.8)×10−3 for Th(HFAA)4 and (3.8±0.4)×10−3 min−1 for Th(DBM)4, (T=92°C, I=3 W cm−2). The rate of the sonochemical reaction increased with the rising β-diketonate volatility and decreased with the rising hydrocarbon solvent vapor pressure. Solid sonication products consisted of a mixture of thorium carbide ThC2 and Th(IV) β-diketonate partial degradation products. The average ThC2 particle size was estimated to be about 2 nm. ThC2 formation was attributed to the high-temperature reaction occurring within the cavitating bubble. The thorium β-diketonate partial degradation products formed in the liquid reaction zones surrounding the cavitating bubbles. 相似文献
In bilayer graphene, mutual rotation of layers has strong effect on the electronic structure. We theoretically study the distribution of electron density in twisted bilayer graphene with the rotation angle of 21.8° and find that regions with AA‐like and AB‐like stacking patterns separately contribute to the interlayer low‐energy van Hove singularities. In order to investigate the peculiarities of interlayer coupling, the charge density map between the layers is examined. The presented results reveal localization of π‐electrons between carbon atoms belonging to different graphene layers when they have AA‐like stacking environment, while the interlayer coupling is stronger within AB‐stacked regions.
Charge density map for bilayer graphene with a layer twist of 21.8° (interlayer region). 相似文献
In this article, we employ the semiclassical Monte Carlo approach to study the spin polarized electron transport in single layer graphene channel. The Monte Carlo method can treat non-equilibrium carrier transport and effects of external electric and magnetic fields on carrier transport can be incorporated in the formalism. Graphene is the ideal material for spintronics application due to very low Spin Orbit Interaction. Spin relaxation in graphene is caused by D'yakonov-Perel (DP) relaxation and Elliott-Yafet (EY) relaxation. We study effect of electron electron scattering, temperature, magnetic field and driving electric field on spin relaxation length in single layer graphene. We have considered injection polarization along z-direction which is perpendicular to the plane of graphene and the magnitude of ensemble averaged spin variation is studied along the x-direction which is the transport direction. This theoretical investigation is particularly important in order to identify the factors responsible for experimentally observed spin relaxation length in graphene. 相似文献
We analyze the influence of contact electrons on quantum transport in a resonant-tunneling diode (RTD), using a many-body density matrix formalism for open systems. We explicitly relate the net current in the RTD to the memory-containing effective interaction between the RTD active region and the contacts. This effect can only be captured if the RTD active region is treated fully as a dynamically open system. 相似文献
The impact of bound states in Landauer‐Büttiker scattering approach to non‐equilibrium quantum transport is investigated. We show that the noise power at frequency ν is sensitive to all bound states with energies ωb satisfying . We derive the exact expression of the bound state contribution and compare it to the one produced by the scattering states alone. The theoretical and experimental consequences of this result are discussed. 相似文献
The Beckmann scalar scattering model based on the Kirchhoff approximation was used to investigate the scattering of light from periodic surfaces whose roughness amplitude is comparable to, and greater than, the illumination wavelength. Solutions by numerical integration were obtained for surfaces of different profiles and of different roughnesses. It was found that the scattering patterns from these surfaces were very different at large roughness amplitudes. As the incident angle was varied on a given surface, it was also observed that the intensity of any individual diffraction order oscillated and the degree of oscillation was directly related to roughness. By utilizing this property, a new procedure could be developed for surface roughness assessment. 相似文献
Almost uniform wide-angle laser irradiation, for use in medical applications, is achieved by roughening chemically the output end of an optical fibre. The angular distribution of the scattered light is studied theoretically using perturbation theory. The theoretical results evaluated from a simple method of calculation are in sufficiently good agreement with experiment. 相似文献