共查询到20条相似文献,搜索用时 31 毫秒
1.
We explore the phenomenon of tunneling in single carrier 2-D quantum dot by quantum adiabatic switching route. The confinement in the y-direction is kept harmonic which ensures that tunneling is allowed only along the x-direction. The harmonic confinement potential is kept fixed and a constant external magnetic field is applied along the z-direction. The growth of probability density in the classically forbidden zones and tunneling current are monitored critically which reveals how tunneling significantly depends on the barrier parameters. The efficacy of the switching function in enforcing adiabaticity of the evolution is demonstrated. The effective mass, barrier width, and height emerge as important control parameters. 相似文献
2.
《Superlattices and Microstructures》1999,26(5):289-297
We study the quantum wave transport in nanoscale field-effect transistors. It has been shown that the tunneling effect between the source and the drain in an ultra-short channel transistor significantly degrades the control of the drain current by the gate. However, the tunneling effect is suppressed by reducing the depth of the source and drain junctions which is designated to suppress the short-channel effects concerning the cut-off characteristics of the field-effect transistor. The reduced junction depth confines the carriers in the direction (y -direction) perpendicular to the transport direction (x -direction). The matching of y -direction wavefunctions at regional boundaries suppresses the tunneling effect and normal FET current–voltage characteristics has been obtained, which explains theoretically the successful fabrication of nanoscale field-effect transistors. 相似文献
3.
We report on the errors obtained by comparing in- and out-of-plane displacements calculated from the sensitivity matrix with all its components, and when only the component from the largest contributing of each one of the three interferometers is considered. Divergent illumination is considered in the evaluation of sensitivity vector to measure displacement vector components. This analysis is performed for a flat elastic target which is loaded in the x-direction and after in the z-direction. The technique applied is electronic speckle pattern interferometry. 相似文献
4.
We calculate the Stark effect and the polarisability of shallow-donor impurity located in the centre of lens shaped quantum dot by a variational method and in the effective-mass approximation. Our theoretical model assumes an infinite confinement to describe the barriers at the dot boundaries and the electric field is considered to be applied in the z-direction. The systematic theoretical investigation contains results with the quantum dot size and the strength of the external field. Our calculations reveal that the interval wherein the polarisability varies depends strongly on the dot size. 相似文献
5.
Ralph Blüthner Barbara Hinz Gerhard Menzel Marianne Schust Helmut Seidel 《Journal of sound and vibration》2006,298(3):627-637
Seats with horizontal suspensions can help to reduce detrimental effects of whole-body vibration (WBV) on health, comfort and performance. Two seats were used to examine the effect of body mass and WBV-magnitude on the transmission of WBV from the seat base to the cushion. Both seats have suspension in the x-direction while Seat 2 has suspension also in the y-direction. Twelve subjects with a body mass ranging from 59.0 to 97.3 kg volunteered for the study. A set of anthropometric characteristics was acquired. Three magnitudes of WBV were used with a truck-like signal (Seat 1, 0.3-0.59 m s−2wd-weighted rms values at the seat base, x-direction) and a tractor-like signal (Seat 2, 0.55-1.09 m s−2wd-weighted rms values at the seat base, x-direction, 0.52-1.07 m s−2wd-weighted rms values, y-direction). The magnitude of WBV had a significant effect on the transmissibility characterized by SEAT-values. A significant influence of the body mass on SEAT-values was found for the y-direction only. Other anthropometric characteristics proved to be more important for the prediction of SEAT values by multiple regressions. There was no significant correlation of SEAT-values, x-direction, with the body mass. Other anthropometric characteristics enabled a satisfactory prediction of SEAT values also for x-direction in several cases. Tests with only two subjects of extreme body mass are not suited to obtain comparable and representative results required for a comparison of different seats with a suspension in the x-direction. The effect of the WBV-magnitude on the WBV-transmissibility should be considered with the design, testing and application of suspended seats. 相似文献
6.
We investigate the anisotropic Heisenberg XXZ spin chain that possesses Dzyaloshinskii–Moriya (DM) interaction and discuss the behavior characteristics of the thermal quantum correlation (thermal quantum discord and thermal quantum entanglement) in the inhomogeneous magnetic field that is manipulated by sinusoidal wave. The results indicate that the DM interaction strengthens the thermal correlation such that the stronger the DM interaction is, the more obvious it strengthens. We can control the thermal correlation through externally adding an inhomogeneous magnetic field that a relative stable range can be formed where the thermal quantum correlation is almost foreign to the coupling coefficient of z-direction spin, thereby the thermal quantum correlation is controlled and enhanced. 相似文献
7.
The magnon energy bands are studied for a four-layer ferromagnetic superlattice, with regard to the effects of the competition between the anisotropy and the spin quantum number. A special attention is also paid on the effects of the symmetry of the system. It is found that three modulated energy gaps exist in the magnon energy band along Kx direction perpendicular to the superlattice plane. The magnetic anisotropy affects significantly the magnon energy gaps. The zero energy gap Δω23 correlates with the conditions between anisotropy constants, D1+D3=D2+D4 and D1=D3 (or D2=D4), while the disappearance of the magnon energy gaps Δω12 and Δω34 corresponds to a translational symmetry of x-direction in a unit cell. When the parameters of the system deviate from these conditions, the energy gaps Δω12, Δω23 and Δω34 become larger. There is a competition effect of the anisotropy and the spin quantum number on the magnon energy gaps Δω12 and Δω23. When the symmetry of the system is higher, the competition can achieve a balance to cause the zero energy gap. 相似文献
8.
Zhengjun Liu Qiuming Li Xiaogang Sun Muhammad Ashfaq Ahmad 《Optics Communications》2009,282(8):1536-5597
Based on 1-D fractional Fourier transform, we proposed an image encryption algorithm in order to hide two images simultaneously. When the fractional order is closed to 1, most energy in frequency domain is centralized in the center part of spectrum. The image can be recovered acceptable by using a half of spectrum, which locates in the middle part at x-direction or y-direction. Cutting operation is employed in order to combine two spectra. Double random phase encoding is employed for image encryption. The corresponding numerical simulations are performed to demonstrate the validity and efficiency of the algorithm. 相似文献
9.
In this paper, the dispersion relations of surface phonon–polaritons in freestanding rectangular quantum wire systems of polar ternary mixed crystals are derived. The numerical calculations for AlxGa1−xAs and ZnxCd1−xSe quantum wire systems are performed. The results reveal that the frequencies of surface phonon–polariton modes are sensitive to the geometric structures of the quantum wires, the wave-vectors in z-direction, and the compositions of the ternary mixed crystal materials. The effects of the “two-mode” and “one-mode” behaviors of the ternary mixed crystals on the surface phonon–polariton modes are also discussed. 相似文献
10.
Raman spectroscopy studies are reported for the RuSr2Eu1.5Ce0.5Cu2O10 (Ru-1222) compound at various temperatures of 300, 250, 200 and 90 K. Three distinct vibrational bands: the first at 110, 140, and 160 cm−1, the second at 295 and 347 cm−1, and third one at 651 cm−1 are seen in Raman spectra of the compound at room temperature. These bands are attached to the Cu atoms’ c-direction, the Ru atoms’ ab-plane stretching and Ru atoms’ c-direction anti-stretching modes. Below 200 K, an extra vibrational mode is also seen at 260 cm−1. Also, with a decrease in temperature, though the Cu vibrational modes remain intact, the Ru atoms’ ab-plane stretching (295 cm−1) and c-direction anti-stretching (651 cm−1) modes shift gradually to higher wave number positions. The frequencies of modes at 260 and 651 cm−1 showed anomalous softening and line-width broadening below 100 K that corroborates well with the spin ordering seen in susceptibility studies. The studied compound is a ferromagnetic superconductor with magnetic ordering of the Ru spins at 200 K and superconductivity below 30 K. A magnetic and electrical transport characterization of the compound is also presented briefly. 相似文献
11.
By employing a variational method of the Pekar-type, which has different variational parameters in the x–y plane and the z-direction, we study the ground and the first excited state energies and transition frequency between the ground and the first excited states of a strong-coupling polaron in an anisotropic quantum dot (AQD) under an applied magnetic field along the z-direction. The effects of the magnetic field and the electron–phonon coupling strength are taken into account. It is found that the ground and the first excited state energies and the transition frequency are increasing functions of the external applied magnetic field. The ground state and the first excited state energies are decreasing functions, whereas transition frequency is an increasing function of the electron–phonon coupling strength. We find two ways of tuning the state energies and the transition frequency: by adjusting (1) the magnetic field and (2) the electron–phonon coupling strength. 相似文献
12.
Ren-fu Yang Young SunNai-li Di Qing-an LiZhao-hua Cheng 《Journal of magnetism and magnetic materials》2007
We have studied the magnetocaloric effect (MCE) in a bilayered La4/3Sr5/3Mn2O7 single crystal with applied field along both ab-plane and c-direction. Due to the quasi-two-dimensional structure, the crystal exhibits a strong anisotropy in the MCE. The difference of magnetic entropy change between two crystallographic directions depends on external magnetic fields and has a maximum of 2 J/kg K. A large low-field magnetic entropy change, reaching 3.2 J/kg K for a magnetic field change of 15 kOe, is observed when the applied field is along ab-plane. This large low-field magnetic entropy change is attributed to the rapid change of magnetization in response to external magnetic fields in the easy magnetizing plane. 相似文献
13.
Thermal entanglement of the two-qubit XXZ model under magnetic fields in arbitrary directions is studied. Both the uniform and nonuniform fields are addressed. For the ferromagnetic case, a magnetic field perpendicular to the z-axis helps to enhance the entanglement or slows down the decrease of the entanglement. For the antiferromagnetic case, there is the revival phenomenon when the magnetic field is uniform and no such phenomenon when the field is uniform in the z-direction and a staggered type in the x-axis. 相似文献
14.
Guoquan Zhou 《Optics Communications》2006,265(1):39-46
Based on the vectorial structure of non-paraxial electromagnetic beam and non-paraxial vectorial moment theory, the relationship of the beam waists, the divergence angles and the beam propagation factors among non-paraxial linearly polarized Gaussian beam, its TE and TM terms have been presented, respectively. The analytical beam propagation factors are given and further discussed at the highly non-paraxial case. The maximum divergence angles in the x-direction of non-paraxial linearly polarized Gaussian beam, its TE and TM terms are all 54.7°, and those in the y-direction are limited to be 63.4°, 67.7° and 39.2°, respectively. As TE and TM terms are orthogonal and can be detached at the far field, the potential applications of the isolated TE and TM terms are deserved further investigation. 相似文献
15.
Ashley M. DaSilva 《Solid State Communications》2011,151(20):1444-1446
With the recent observation of graphene-like Landau levels at the surface of topological insulators, the possibility of fractional quantum Hall effect, which is a fundamental signature of strong correlations, has become of interest. Some experiments have reported intra-Landau level structure that is suggestive of fractional quantum Hall effect. This paper discusses the feasibility of fractional quantum Hall effect from a theoretical perspective, and argues that while this effect should occur, ideally, in the n=0 and |n|=1 Landau levels, it is ruled out in higher |n| Landau levels. Unlike graphene, the fractional quantum Hall effect in topological insulators is predicted to show an interesting asymmetry between n=1 and n=−1 Landau levels due to spin-orbit coupling. 相似文献
16.
E. Kasapoglu H. Sari I. Sokmen 《Physica E: Low-dimensional Systems and Nanostructures》2003,19(4):332-335
We have studied theoretically the impurity binding energy for wires of different shapes (V-shaped quantum wire (V-QWR) and rectangular wire) with a variational procedure without using any coordinate transformation. The effective potential for V-QWR used in this work consists of a square well potential in the z-direction and full graded well potential in the x-direction. Our results are in good agreement with previous theoretical results, found by the coordinate transformation method. Furthermore, it is shown that the impurity binding energy in quantum wires is sensitive to the geometrical effects. 相似文献
17.
Halil Tanyer Eyyubo?lu 《Optics Communications》2007,272(1):22-31
For a generalized beam at the source plane passing through co-located aperture and a propagation path consisting of an off-axis x-y asymmetric ABCDGH system, the receiver plane irradiance expression is derived using the Collins integral. A collection of source beam profiles that are obtainable from the generalized beam formulation are illustrated. Plots are given for viewing the progress of selected generalized beam types along the propagation axis, containing a single thin lens, co-centric and misaligned in the x-direction. The received power falling onto a finite aperture surface is calculated for various misalignment situations. 相似文献
18.
The nature of the pseudogap state and its relation to the d-wave superconductivity in high-T c superconductors is still an open issue. The vortex-like excitations detected by the Nernst effect measurements exist in a certain temperature range above superconducting transition temperature T c, which strongly support that the pseudogap phase is characterized by finite pairing amplitude with strong phase fluctuations and imply that the phase transition at T c is driven by the loss of long-range phase coherence. We first briefly introduce the electronic phase diagram and pseudogap state of high-T c superconductors, and then review the results of Nernst effect for different high-T c superconductors. Related theoretical models are also discussed. 相似文献
19.
Linear properties of obliquely propagating magnetosonic waves (both fast and slow) in multicomponent (electron-positron-ion (e-p-i) and dust-electron-ion (d-e-i)) quantum magnetoplasma are studied. It is found that the quantum Bohm potential term significantly changes the propagation of fast and slow magnetosonic waves in both e-p-i and d-e-i quantum plasmas. The variation of the dispersion characteristics with the increase/decrease of positron concentration in e-p-i and dust concentration in d-e-i quantum magnetoplasma is explored. Finally, the effect of angle θ (that the ambient magnetic field makes with the x-axis) on the dispersion properties of magnetosonic waves in multicomponent quantum magnetoplasma is investigated. The relevance of the present investigation to the dense astrophysical environments and microelectronic devices is also pointed out. 相似文献
20.
J. Barba-Ortega J. Albino Aguiar 《Physica C: Superconductivity and its Applications》2009,469(13):754-755
The time dependent Ginzburg–Landau equations (TDGLE) are used to study the properties of a mesoscopic superconducting square surrounded by different metallic materials. The properties of the metallic environment are taken into account by De Gennes boundary conditions, via the extrapolation length b. The external magnetic field is applied perpendicularly to the square surface. The TDGLE are used upon taking the magnetic field and the order parameter invariant along z-direction. It is determined the b-limit for the occurrence of a single vortex in a mesoscopic square of area d2, d varies discretely from 4ξ(0) to 10ξ(0). We can show a logarithmical dependence of the sample size as a function on b parameter. 相似文献