Tunneling in 2-D quantum dots via quantum adiabatic switching route

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.     

Suppression of the tunneling effect by shallow junctions in field-effect transistor

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.     

Evaluation of error in the measurement of displacement vector components by using electronic speckle pattern interferometry

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.     

Stark-shift of impurity fundamental state in a lens shaped quantum dot

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.     

Effects of competition between the anisotropy and the spin quantum number on the magnon energy gap in a four-layer ferromagnetic superlattice

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 K_x 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.     

Influence of Dzyaloshinskii–Moriya interaction in the sinusoid magnetic field on the thermal quantum correlation of inhomogeneous Heisenberg spin chain

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.     

A new kind of double image encryption by using a cutting spectrum in the 1-D fractional Fourier transform domains

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.     

On the significance of body mass and vibration magnitude for acceleration transmission of vibration through seats with horizontal suspensions

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⁻²w_d-weighted rms values at the seat base, x-direction) and a tractor-like signal (Seat 2, 0.55-1.09 m s⁻²w_d-weighted rms values at the seat base, x-direction, 0.52-1.07 m s⁻²w_d-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.     

Surface phonon–polaritons in rectangular quantum wires of polar ternary mixed crystals

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 Al_xGa_1−xAs and Zn_xCd_1−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.     

Magnetic field effect on state energies and transition frequency of a strong-coupling polaron in an anisotropic quantum dot

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.     

Raman spectroscopy of RuSr2(Eu1.5Ce0.5)Cu2O10 magneto-superconductor

Raman spectroscopy studies are reported for the RuSr₂Eu_1.5Ce_0.5Cu₂O₁₀ (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.     

Vectorial structures of non-paraxial linearly polarized Gaussian beam and their beam propagation factors

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.     

Anisotropic and large low-field magnetic entropy change in a La4/3Sr5/3Mn2O7 single crystal

We have studied the magnetocaloric effect (MCE) in a bilayered La_4/3Sr_5/3Mn₂O₇ 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.     

Influence of arbitrary magnetic field on entanglement in Heisenberg XXZ model

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.     

The stability of the fractional quantum Hall effect in topological insulators

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.     

Geometrical effects on shallow donor impurities in quantum wires

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.     

Generalized beams in ABCDGH systems

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.     

De Gennes parameter limit for the occurrence of a single vortex in a square mesoscopic superconductor

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.     

The vortex-like excitations detected by Nernst signals in high-T c superconductors

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.     

Dynamics of Quantum Dissonance of Two Qubit XXZ Model with Dzyloshinsky-Moriya Interaction Coupled to Non-Markovian Environment

We consider the dynamics of quantum correlations of two coupled spin qubits with Dzyaloshinsky-Moriya (DM) interaction influenced by a local external magnetic field along the z-direction and coupled to bath spin- $\frac{1}{2}$ particles as independent non-Markovian environment. For this model, we calculate the entanglement measure of concurrence, quantum discord and quantum dissonance and find effects of DM interaction, bath-system coupling constant and temperature on the dynamics of quantum correlation. At last, we obtain the teleportation for this model by using fidelity and observe changes of DM interaction, bath-system coupling constant, temperature and magnetic field on fidelity.