Nonlocal heat transfer in nanostructures

Kinetics of electrons in a degenerate conductor heated up by absorption of a high-frequency field localized in a region of about hundred nanometers has been studied. A new law for nonlocal electron thermal flux has been predicted.     

氢负离子在磁场和金属面附近电子通量分布的研究

利用半经典开轨道理论, 研究了磁场和金属面附近氢负离子的剥离电子通量分布, 并揭示了电子通量分布中的振荡结构与经典轨道之间的关系.固定离子到金属面的距离, 研究了不同的磁场强度对电子通量分布的影响. 结果表明, 由于与电子通量分布相联系的剥离电子的经典轨迹增加, 随着磁场强度的增加, 通量分布变得复杂. 此外发现剥离电子的能量变化也会影响电子通量分布. 因此可以通过改变磁场强度大小和剥离电子的能量来调控剥离电子通量分布和干涉图样. 研究结果对于理解负离子在外场、表面附近的电子流通量和剥离电子干涉图样问题以及将来实验研究负离子的光剥离显微问题都可以提供一定的参考. 关键词： 开轨道理论 电子通量 金属面 磁场     

Electron Flux Distributions in the Photodetachment of H2- in an Electric Field

The electron flux distributions in the photdetachment of a negative hydrogen molecular ion in an electric field have been studied by using the two-center model and the dosed orbit theory. An analytic formula is presented for the electron flux of H2 in the presence of an electric field. The results show that the interference between the two orbits passing through the given spatial point leads to the oscillation in the electron flux distribution. Besides, the interference between the two centers of the H2^- is also very important. The comparison between the electron flux of H2^- in electric field with the result of H^- shows that at the equilibrium distance of two centers in the H2^-, the interference of the two nuclei on the detached electron＇s flux distribution is very strong, while at larger distance of the two centers, the interference effect of the two centers is decreased.     

Photodetachment of HF- in an Electric Field

Photdetachment of a negative HF^- ion in an electric field is studied by using the two-centre model and the closed orbit theory. An analytic formula is presented for the electron flux of HF^- in the presence of an electric field. The results show that the oscillation in the electron flux distribution is caused by the rescattering effect of the molecular ion core and the interference between the two nuclei. In addition, the interference between the orbits passing through the given spatial point also plays an important role in the electron flux distribution. This study provides a new understanding of the photodetachment of polar molecules in the presence of external field.     

Direkte Beobachtung einzelner magnetischer Flußquanten in supraleitenden Hohlzylindern. III

By use of electron interferometry the trapped magnetic flux was investigated in superconducting microcylinders (inner diameter < 1 μm). Even in thin walled cylinders (wall thickness < penetration depth) at temperatures near the superconducting transition the flux was found to be quantized in integer multipleshc/2e. In the appendix an interpretation of the magnetic Aharonov-Bohm effect as a local interaction between the excluded field and the electromagnetic field of the electron is discussed.     

High-frequency breakdown and paschen law

In the present paper an attempt has been made to draw theoretically a correlation between the well-known Paschen curve and the high-frequency breakdown characteristic of a gas device by interpreting electron mean free path in terms of the frequency of the applied field. The analytical high-frequency breakdown characteristic, so obtained, agree fairly well with the experimental results.     

A possible interplay between electron beams and magnetic fluxes in the Aharonov–Bohm effect

Most studies on the magnetic Aharonov–Bohm (A–B) effect focus on the action exerted by the magnetic flux on the electron beam, but neglect the back-action exerted by the electron beam on the magnetic flux. This paper focuses on the latter, which is the electromotive force ΔU across the solenoid induced by the time-dependent magnetic field of the electron beam. Based on the backaction analysis, we observe that the magnetic A–B effect arises owing to the interaction energy between the magnetic field of the electron beam and the magnetic field of the solenoid. We also demonstrate that the interpretation attributing the magnetic A–B effect to the vector potential violates the uncertainty principle.     

High intensity of interband transitions in double-barrier structures with a high-frequency electric field

A solution of a two-band analogue of the time-dependent Schrödinger equation describing resonance coherent electron interaction with a high-frequency field was found for a symmetric double-barrier structure, and an analytic expression was obtained for the small-signal conductivity proportional to the electron transition intensity. It was found that the high-frequency conductivity of double-barrier structures in the case of interband transitions could be significantly higher than in the case of intersubband transitions.     

Mode-selective amplification in a waveguide free electron laserwith a two-sectioned wiggler

One important issue in waveguide free electron lasers (FELs) involves an interaction of the electron beam with one waveguide mode at two different resonant frequencies. Since the low-frequency mode often has a higher pain, the usually preferred high-frequency mode is suppressed as a result of mode competition. In this paper, possible control of this mode competition is considered using a nonstandard wiggler magnet consisting of two cascaded wiggler sections with different periods and field strengths. It is demonstrated that with an appropriate differentiation between the two wiggler sections the high-frequency mode may be amplified preferentially. This mode-selective amplification may be used to suppress the low-frequency mode. A small signal gain formulation is developed for a waveguide FEL with such a two-sectioned wiggler arrangement and numerical examples are used to demonstrate its applicability to mode control in waveguide FELs. Effects of wiggler field errors and electron energy spread are also considered. It is shown that the requirement for wiggler field errors and electron energy spread in the two-sectioned wiggler arrangement is similar to that in the usual straight wiggler configuration     

Photodetachment microscopy of the hydrogen negative ion in electric field near a metal surface

According to the semi-classical theory, we study the photodetachment microscopy of H^- in the electric field near a metal surface. During the photodetachment, the electron is photo-detached by a laser and the electron is drawn toward a position-sensitive detector. The electron flux distribution is measured as a function of position. Two classical paths lead the ion to any point in the classically allowed region on the detector, and waves traveling along these paths produce an interference pattern. If the metal surface perpendicular to the electric field is added, we find that the interference pattern is related not only to the electron energy and the electric-field strength, but also to the ion--surface distance. Besides, the laser polarization also has a great influence on the electron flux distribution. We present calculations predicting the interference pattern that may be seen in experiment. We hope that our study can provide a new understanding of the electron flux distribution of negative ions in external field and surface, and can guide the future experimental research on the negative ion photo-detachment microscopy.     

Scattering of spin-polarized electron in an Aharonov-Bohm potential

The scattering of spin-polarized electrons in an Aharonov-Bohm vector potential is considered. We solve the Pauli equation in 3 + 1 dimensions taking into account explicitly the interaction between the three-dimensional spin magnetic moment of electron and magnetic field. Expressions for the scattering amplitude and the cross section are obtained for spin-polarized electron scattered off a flux tube of small radius. It is also shown that bound electron states cannot occur in this quantum system. The scattering problem for the model of a flux tube of zero radius in the Born approximation is briefly discussed.     

Photo-Detached Electron Flux Distribution in a Gradient Electric Field

This paper investigates the flux distributions of the electron photo-detached from H-ion localized in a gradient electric field. In contrast with the photodetachment in the uniform electric field [Phys. Rev. A 40(1989) 4983],where only two electron trajectories interfere at each given point on a detector, for the photodetachment in a gradient electric field, the electrons waves can travel along multiple paths from the negative ion to a given point on the detector plane, which makes the electron flux distributions on the detector plane become much complex. Using the semi-classical theory, we put forward a formula for calculating the electron flux. Our calculation results suggest that the electron flux distributions on a given detector plane is not only related to the propagation time of the detached electron, but also related to the detached electron's energy. With the increase of the detached electron's energy, the oscillating region in the electron flux distributions becomes enlarged and the oscillating structure in the flux distributions becomes much more complicated. This study will guide future experiment research on the photodetachment microscopy of the negative ions in the presence of non-uniform external fields.     

Terahertz conductivity and possible BLOCH gain in semiconductor superlattices

We have investigated terahertz emission due to dynamical electron transport in wide-miniband GaAs/Al(0.3)Ga0.7As superlattices. By noting that the time-domain THz emission spectroscopy inherently measures the step-response of the electron system to the bias electric field, the obtained THz spectra were compared with the high-frequency conductivities predicted for miniband transport. Excellent agreement between theory and experiment strongly supports that the THz gain due to Bloch oscillating electrons persists at least up to 1.7 THz. It was also found that Zener tunneling into the second miniband sets the high-frequency limit to the THz gain for the samples studied here.     

Quantum theory of electron motion in a cyclic resonant accelerator

The motion of a relativistic electron in a constant focusing magnetic field and a high-frequency rotational electromagnetic field, used to offset the radiative energy loss, is studied on the basis of the Klein-Gordon equation. The solutions found may be used to construct a theory for electron storage rings, in which quantum fluctuations are particularly important.Translated from Izvestiya VUZ. Fizika, No. 4, pp. 12–22, April, 1970.     

Relativistic theory of atom-laser interactions at very high laser intensities

The high-frequency approximation of Kristi? and Mittleman is considered in detail as a basis for the relativistic theory of atom-laser interactions. The properties of the 3D potentials are discussed. Within a one-dimensional model similar to that employed by Kylstra, Ermolaev, and Joachain in ab initio calculations on the time-dependent Dirac equation, the electron mass-shift due to dressing by a superstrong laser field is investigated. In the full domain of the laser parameters, the frequency ω and the peak field strength ?₀, the 1D bound states exhibit remarkable features. The numerical calculations show the existence of a very wide intermediate range of the field strengths where, in the zeroth order of the high-frequency approximation, the binding is stabilized by the field.     

Zero bias conductance peak in InAs nanowire coupled to superconducting electrodes

We report the occurrence of the zero-bias conductance peak (ZBCP) in an InAs nanowire coupled to PbIn superconductors with varying temperature, bias voltage, and magnetic field. The ZBCP is suppressed with increasing temperature and bias voltage above the Thouless energy of the nanowire. Applying a magnetic field also diminishes the ZBCP when the resultant magnetic flux reaches the magnetic flux quantum h/2e. Our observations are consistent with theoretical expectations of reflectionless tunneling, in which the phase coherence between an electron and its Andreev-reflected hole induces the ZBCP as long as time-reversal symmetry is preserved.     

氢负离子剥离电子通量的数值研究

本论文利用杜,赵等人的半经典轨道理论,推导了电场和金属面同时存在时,氢负离子的剥离电子通量分布,并对干涉图样进行了数值模拟。结果发现剥离电子通量分布不仅与激光光子能量和外场有关,并且敏感地依赖于金属面与氢负离子之间的距离。这些结果可以应用于许多重要的研究领域,包括超快激光表面催化,更准确的测量电子亲和力和控制低能的光电子和表面的相互作用等。     

氢负离子剥离电子通量的数值研究

本论文利用杜,赵等人的半经典轨道理论,推导了电场和金属面同时存在时,氢负离子的剥离电子通量分布,并对干涉图样进行了数值模拟。结果发现剥离电子通量分布不仅与激光光子能量和外场有关,并且敏感地依赖于金属面与氢负离子之间的距离。这些结果可以应用于许多重要的研究领域,包括超快激光表面催化,更准确的测量电子亲和力和控制低能的光电子和表面的相互作用等。     

On the feasibility of the coulomb explosion of a metal

The mechanism of the Coulomb explosion of a metal in an external pulsed electric field is discussed. In the case of a low-frequency field, when its frequency is lower than the frequency of electron collisions, it is impossible to reach the conditions of the Coulomb explosion of a metal if the field pulse duration is shorter than the time of electron energy relaxation upon elastic collisions, and the electron temperature is well above the Fermi energy and the work function. In the case of a high-frequency field, e.g., in a powerful pulse of ultraviolet laser radiation, the Coulomb explosion can occur if the field strength is well above the intraatomic field strength (i.e., when the laser power density is ≥10¹⁹ W/cm²).     

Numerical study on discharge characteristics influenced by secondary electron emission in capacitive RF argon glow discharges by fluid modeling

A one-dimensional(1D) fluid model of capacitive RF argon glow discharges between two parallel-plate electrodes at low pressure is employed. The influence of the secondary electron emission on the plasma characteristics in the discharges is investigated numerically by the model. The results show that as the secondary electron emission coefficient increases,the cycle-averaged electric field has almost no change; the cycle-averaged electron temperature in the bulk plasma almost does not change, but it increases in the two sheath regions; the cycle-averaged ionization rate, electron density, electron current density, ion current density, and total current density all increase. Also, the cycle-averaged secondary electron fluxes on the surfaces of the electrodes increase as the secondary electron emission coefficient increases. The evolutions of the electron flux, the secondary electron flux and the ion flux on the powered electrode increase as the secondary electron emission coefficient increases. The cycle-averaged electron pressure heating, electron Ohmic heating, electron heating, and ion heating in the two sheath regions increase as the secondary electron emission coefficient increases. The cycle-averaged electron energy loss increases with increasing secondary electron emission coefficient.