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We propose a simple single-layer magnetic microtrap configuration which can trap an array of magnetically-trapped Bose-Einstein condensate. The configuration consists of two series of parallel wires perpendicular to each other and all of the crossing points are cut off for maintaining the uniformity of the current. We analyse the trapping potential, the position of trapping centres and the uniformity of the array of the traps. The trapping depth and trapping frequency with different parameters are also calculated. Lastly, the effect of the cut-off crossing points, dissipate power, chip production are introduced concisely.

We report an experiment of trapping of neutral Rb-87 atoms on a, self-made atomchip. The H-shaped atomchip is made by magnetron sputtering technology, which is different from the atomchip technology of other teams. We collect 3 x 10(6) Rb-87 atoms in the mirror magneto-optical trap (MOT) using the external MOT coils, and 1 X 10(5) Rb-87 atoms are transferred to U-MOT using U-shaped wire in chip and a pair of bias coils.

We propose a simple method to calculate the spectrum of spontaneous terahertz (THz) emission from hot carriers in two-dimensional semiconductors by means of transport quantities, which are easily obtained during the process of solving the transport problem using the recently developed balance-equation approach for THz-driven transport. The method has been applied to examine the surface emission from a GaAs/AlGaAs heterojunction and the edge emission from a GaAs-based multiple quantum-well system subjected to strong dc biases. The theoretical results obtained are in reasonably good agreement with measurements.

We present a detailed theoretical and numerical investigation on nonlinear transport of a model three-dimensional electron gas driven by an intense terahertz (THz) radiation at lattice temperature using the conventional and recently developed balanceequation approach. Ionized-impurity, acoustic-phonon and polar optical-phonon scatterings were taken into account for electrons in a single parabolic band. The heating of electrons and the suppression of the dc electron mobility by the irradiation of the intense THz field are predicted. We find that the dc average mobility of electrons peaks around a certain value of the amplitude of the ac field at low lattice temperature.

On the basis of the Lei–Ting balance-equation transport theory recently developed for nonparabolic energy band, we propose a hydrodynamic approach to the spatially inhomogeneous electron transport in semiconductor devices. In the present approach, the momentum and energy collision terms are expressed by two nonlinear functions, the frictional acceleration and energy-loss rate, which give a detailed scattering-process-level description of nonstationary and nonlocal charge transport in the system. This approach allows one to calculate selfconsistently the transport parameters within the model itself based on the primary material data (band structure, deformation potential constant, etc.), thus it minimizes the uncertainty associated with the use of some empirical relations for transport coefficients. As a demonstration of the approach, we have carried out a numerical calculation for a submicrometer Si diode by assuming an isotropic Kane-type energy band. The results for electron velocity and energy, obtained at much less computing cost than the Monte–Carlo (MC) method, are in good agreement with MC prediction. The influence of heat-flow term on electron transport behaviour, especially on velocity overshoot, is also investigated.

The possible absolute instability in superlattice miniband transport using the hydrodynamic balance equations for arbitrary energy dispersion is investigated. In contrast to the prediction of the drift-diffusion model that in doped semiconductor superlattices absolute instability occurs closely following the onset of negative differential mobility (NDM), the present analysis shows that a wide-miniband planar superlattice may become absolutely unstable only when it is biased deep in the NDM regime. This result is in agreement with recent experimental findings.

We present an alternative scheme to exactly implement one-qubit and two-qubit quantum gates with a single trapped cold ion driven by a travelling laser field. The internal degree of freedom of the ion acts as the target qubit and the control qubit is encoded by two Fock states of the external vibration of the ion. The conditions to realize these operations, including the duration of each applied laser pulse and Lamb-Dicke parameter, are derived. In our scheme neither the auxiliary atomic level nor the Lamb-Dicke approximation is required. The multiquantum transition between the internal and external degrees of freedom of the ion is considered.

We investigate nonlinear thermal transport properties of a single interacting quantum dot with two energy levels tunnel-coupled to two electrodes using nonequilibrium Green function method and Hartree-Fock decoupling approximation. In the case of asymmetric tunnel-couplings to two electrodes, for example, when the upper level of the quantum dot is open for transport, whereas the lower level is blocked, our calculations predict a strong asymmetry for the heat (energy) current, which shows that, the quantum dot system may act as a thermal rectifier in this specific situation., Comment: 5 pages, 5 figures

We report our studies of zero-frequency shot noise in tunneling through a parallel-coupled quantum dot interferometer by employing number-resolved quantum rate equations. We show that the combination of quantum interference effect between two pathways and strong Coulomb repulsion could result in a giant Fano factor, which is controllable by tuning the enclosed magnetic flux., Comment: 11 pages, 2 figures

We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to two ferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach. We first develop a Bloch-type equation microscopically to describe the cotunneling-induced spin relaxation dynamics, and then develop explicit analytical expressions for the local magnetization, current, and its fluctuations. On this basis, we predict a novel zero-bias anomaly of the differential conductance in the absence of a magnetic field for the anti-parallel configuration, and asymmetric peak splitting in a magnetic field. Also, for the same system with large polarization, we find a negative zero-frequency differential shot noise in the low positive bias-voltage region. All these effects are ascribed to rapid spin-reversal due to underlying spin-flip cotunneling., 7 pages, 5 figures, submitted

We investigate the linear and nonlinear transport through a single level quantum dot connected to two ferromagnetic leads in Kondo regime, using the slave-boson mean field approach for finite on-site Coulomb repulsion. We find that for antiparallel alignment of the spin orientations in the leads, a single zero-bias Kondo peak always appears in the voltage-dependent differential conductance with peak height going down to zero as the polarization grows to P=1. For parallel configuration, with increasing polarization from zero, the Kondo peak descends and greatly widens by the appearance of shoulders, and finally splits into two peaks on both sides of the bias voltage around $P\sim 0.7$ until disappears at even larger polarization strength. At any spin orientation angle $\theta$, the linear conductance generally drops with growing polarization strength. For a given finite polarization, the minimum linear conductance always appears at $\theta=\pi$., Comment: 7 pages, 8 figures

We examine the temperature dependence of acoustic-phonon-induced magnetoresistance oscillations in a high-mobility GaAs-based quantum well with conventional transverse and longitudinal phonon modes, using a model in which the temperature increase of the Landau level broadening or the single-particle scattering rate 1/τs is attributed to the enhancement of electron-phonon scattering with rising temperature. The non-monotonic temperature behavior, showing an optimal temperature at which a given order of oscillation amplitude exhibits a maximum and the shift of the main resistance peak to higher magnetic field with rising temperature, is produced, in agreement with recent experimental findings.

We present a theoretical study of quasi-classical transport of two-dimensional Bloch electrons under the influence of an electric and a magnetic fields, starting respectively from the quasi-classical equation of motion of electrons and from the balance equations proposed by one of the authors. The electron longitudinal velocity vx and the Hall drift velocity vy are calculated as functions of the magnetic field under different strengths of the applied electric field. It is shown that both vx and vy always change continuously with variation of magnetic field. No sudden jump in the vx-B or the vy-B curve has been found at any given electric field, in contradiction with the claim made in a recent paper published in Acta Physica Sinica (vol. 46). The possible cause for this disagreement is discussed. Furthermore, we point out that the validity of the naive way to study electron transport by directly introducing a damping force into the quasi-classical equation of motion of electron is quite limited.

Balance equations are established for steady-state nonlinear electronic transport in the presence of an electric field in a type-II superlattice, which is modelled by periodically arranged electron-hole bi-layers of finite thickness. Both carrier-phonon and carrier-impurity scatterings, as well as electron-hole interaction, are taken into account. The approach is also extended to the discussion of high-frequency linear transport of the system. The general equations-for determining the current density are obtained and the explicit expressions for complex dynamical resistivity due to electron-hole coupling are given.

It is suggested that the extremely large oxygen isotopic Tc shift recently reported in YBa2Cu3O7 may not be an intrinsic mass effect related to the mechanism but due to the small difference of the oxygen contents.

The Ziman-type theory of the electrical resistivity of liquid metals is extended to disordered crystalline alloys by means of a prescription given by Baym. The formulae for calculating the resistivity of these systems are presented and the temperature dependence of the resistivity in both low and high temperature range is discussed in some detail. By using the Debye model for lattice vibration, we can express the resisti-vity of a disordered system as ρ=ρ0+ρd(T/Θ)2+ρi(T/Θ)5 at temperatures well below Debye temperature,Θ , this behavior is compatible with experiments. On account of the Debye-Waller factor and multi-phonon effects, the resistivity approaches saturation at high temperature instead of the exhibiting a linear T-dependence predicted by onephonon approximation. A comparison between experimental data and a simple expression derived on the basis of the approximation of independent vibration of atom shows that the deviation from linearity of the high temperature resistivity similar to that of Nb can be understood with the present model.

On the basis of a recent discussion on the analytical properties of the first order equation for Tc, we show, by concrete examples, that the radius of convergence of the series for superconducting critical temperature is so sensitive to the high-frequency behaviors of the phonon spectral function, that it is inadequate for it to serve as a critical quantity in the criterion for dividing superconductors into type A and type B.

A new approach to nonlinear electronic transport in solids is described briefly and is applied to the discussion of combined acoustic and optical phonon. scattering. It is found that although a relatively flat region may exist in the currenit-versus-field curve if the scattering by optical phonon is strong, the saturation of the current density, which occurs in the case of pure optical scattering, disappears and the acoustic phon-ons are always important at high current density.

We have discussed the effect of the split of the energy levels between spin-up and spin-down electrons caused by magnetization on the magnon-induced resistivity in ferromagnetic metals at low temperatures. As a result of such an energy split, the low-temperature magnetic resistivity always declines exponentially with decreasing temperature in the single-hand model, while it may probably be enhanced in certain conditions in the two-band model. The comparison between the low-temperature expression of magnetic resistivity deduced from the single-band model considering the energy-gap in the spin-wave spectrum and the experimental data of Tb and Dy shows agreement not only on temperature dependence of resistivity at low temperatures but on the magnitude of high-temperature magnetic resistivity as well.

The linearized Eliashberg equations for a superconductive system in strong exchange fields have been investigated. An iteration procedure has been used for including the asymmetry of the gap function φ(ω) with respect to ±ω and an approximate solu-tion has been obtained in the lowest order of the iteration equation. The results show that the asymmetry in the gap function can considerably change the critical exchange field as a function of temperature in moderate or stronger electron-phonon coupling (λ≥ 0.5) systems.

It is pointed out that zph≡F(-ωph-2 is generally a branch point of the inverse function of the function z=F(y)≡∫0(ωph)(ω2y)/(ω2y+1)g(ω)dω, where g(ω) is the normalized effective phonon spectral function of the system. There-fore it should be taken into account in evaluating the radius of convergence of the series for superconducting critical temperature of the system.

The Ziman-type resistivity theory developed in reference [1] for disordered crystalline alloys is extended to the systems in which the long range order exists, so that it can be applied to the crystalline pure metals and ordered and disordered substitutional alloys. On the basis of this theory, we have investigated the temperature dependence of the resistivity in these systems within the one-phonon approximation. It is emphasized that the superstructure peaks in the structure factors of alloys would give a significant contribution to their phonon-induced electrical resistivity. On account of its T2 behavior and its being much larger than that due to electron-electron scattering, the electron-phonon resistivity contributed by superstructure peaks would play an important role in the temperature dependence of resistivity in alloys, which behaves as ρ≈ρ0+ρa(T/Θ)2+ρi(T/Θ)5 in a relatively low temperature range. Therefore the anomaly in low temperature resistivity of some A-15 compounds can easily be explained with our model. As an example, the low temperature expression for resistivity of alloys is fitted to the V3Si data of Milewits, the theory is found to be in good agreement with experimental results.

Following the idea put forward by Balseiro and Falicov, we have calculated the renor-malized spectral function A (ω) of the amplitude mode of Charge-Density-wave (CDW) phonon by electron-phonon interaction in a model system with coexisting CDW and superconductivity. The A(ω) obtained shows a havily weighted peak of delta-function type at the frequency ω≤2G, where G is the CDW band gap, and a relatively broad continuous spectrum in the region ω>2(G2十△2)1/2, where △ is the superconducting energy gap. Under the condition of fixed G, as △ decreases the intensity of the peak decreases considerably with only a small shift in its position, while the weight of the continuous spectrum raises. These characteristics are in agreement with the behavior of the Raman-active gap modes found by Sooryakumar and Klein in CDW superconductor 2H-NbSe2.

Based on a discussion on the analytical properties of the complex function Fα(y)=∫0(ωph-α)(ω2y)/(ω2y+1)g(ω)dω, we suggest that the partial sum of the Tc series solution proposed by Wu Hang-sheng et al., as an approximate expression for superconducting critical temperature, may still work fairly well within certain range of 1/λ greater thanthe radius of convergence which is limited by the singular point zph. However, the error of the expression that depends upon the highfrequency behavior of the effective phonon spectral g(ω), can not be made infinitely small.

The formulas deduced in reference [6] for the electrical resistivity of substitu-tional alloys are applied to binary stoichiometric and completely ordered A-15 compounds. The comparison between theoretical expressions and experimental data shows that the main characteristics in the temperature dependence of resistivity in various types of A-15 compounds at low temperatures could be understood within the framework of [6], in spite of that there are remarkable differences between these two cases.

In this paper, an explanation for the increase in temperature coefficient of electrical resistivity of Cu3Au with increasing degree of long-range order is given on the basis of a recent theory of resistivity for crystalline alloys proposed by the author. The ρT and dρ/dT of Cu3Au calculated by using a simple model pseudopotential appear to be in relatively good agreement with experimental data.