The geometric potential of a double-frequency corrugated surface

For an electron confined to a surface reconstructed by double-frequency corrugations, we give the effective Hamiltonian by the formula of geometric influences, obtain an additive scalar potential induced by curvature that consists of attractive wells with different depth. The difference is generated by the multiple frequency of the double-frequency corrugation. Subsequently, we investigate the effects of geometric potential on the transmission probability, and find the resonant tunneling peaks becoming rapidly sharper and the transmission gaps being substantially widened with increasing the multiple frequency. As a potential application, double-frequency corrugations can be employed to select electrons with particular incident energy, as an electronic switch, which are more effective than a single-frequency ones.     

On the interaction of a hydrogen atom with a lithium metal surface

In this paper we adopt a molecular cluster approach to study the interaction of a hydrogen atom with a (100) surface of solid lithium metal. In this study, the spin-unrestricted Hartree-Fock equation is solved for the molecular cluster. We also solve for the potential energy surface of the LiH molecule and the Li₂ molecule. We find that the essential features of the hydrogen surface interaction can be understood in terms of the molecule two body interactions. We also find that the hydrogen atom sits below the surface of the Li metal rather than above the surface.     

The interaction between an atom and a surface at large separation

A simple expression is generated for the coefficient C₃ of the asymptotic dispersion interaction ~z^?3 between an atom and a surface. The basis of the derivation is the assumption of simple forms for the frequency dependence of the polarizability of the atom and the dielectric function of the solid. The expression yields the known value of C₃ within a few percent for all cases for which it has been calculated previously. We use it to generate C₃ values for a large number of systems not previously treated.     

Van der Waals interaction between an atom and a surface defect

A continuum dielectric theory is used to investigate the Van der Waals interaction between an atom and a point defect on a planar surface. A vacancy (or adsorbed atom) is modelled by a hemispherical pit (or bump) which perturbs the dielectric response of the defect-free surface. The anisotropy of the interaction is found to be qualitatively different for the vacancy and adsorbate situations. The estimated magnitude of the interaction seems consistent with recent experimental results.     

Parameters of the potential well of an off-center Ge atom in a GeTe-SnTe solid solution

An method is proposed for determining the shape of the three-dimensional multiwell potential of an off-center atom from EXAFS data. The parameters of the potential well of a Ge atom in GeTe and Sn_1?x Ge _x Te (x ≥ 0.4) are determined in the classical and quantum-mechanical approximations. The potential-well depth is varied in the interval 20–40 meV depending on the Ge content, which indicates that the phase transition in these crystals is intermediate in character between the displacement and order-disorder transitions. From analyzing the conditions for the applicability of the classical approximation, it follows that quantum effects must be taken into account in determining the parameters of the potential well of an off-center Ge atom in Sn_1?x Ge _x Te. Quantum-mechanical calculations show that the energy of the lower level in the vibration spectrum of the Ge atom coincides with the maximum energy in the potential well to within several millielectronvolts. The high probability of tunneling or an over-barrier transition of the off-center atom between the potential-well minima prevents dipole reorientations from being frozen at low temperatures.     

Effects of an electric field on the confined hydrogen atom in a parabolic potential well

Using the perturbation method, the confined hydrogen atom by a parabolic potential well is investigated. The binding energy of the confined hydrogen atom in a parabolic potential well is calculated as a function of the confined potential radius and as a function of the intensity of an applied electric field. It is shown that the binding energy of the confined hydrogen atom is highly dependent on the confined potential radius and the intensity of an applied electric field.     

On the interaction of an electron with a nonspherical atom

A three-stage scheme for the excitation of the autoionization state of europium atoms is realized, and the corresponding ionization cross section is determined: σ=6.5×10^?10 cm². Analytical signals from europium atoms are recorded in standard and waste water solutions used in mining noble metals and in the diagnostics of rare-earth elements.     

Potential of interaction of an Ar atom with a proton

The potential of interaction of an Ar atom with a proton is calculated. To verify the result obtained, the wave numbers of the vibrational-rotational spectral lines and the spectroscopic constants for the X¹Σ⁺ state of the ⁴⁰ArH⁺ molecular ion are calculated. The calculated wave numbers of the spectral lines and molecular constants are compared with experimental data.     

Adiabatic tunneling of Bose–Einstein condensates with modulated atom interaction in a double-well potential

We study the adiabatic tunneling of Bose–Einstein condensates in a symmetric double-well potential when the interaction strength between the atoms is modulated linearly or in a cosine periodic form. It is shown that the system evolves along a nonlinear eigenstate path. In the case of linear modulation under the adiabatic approximation conditions, the tunneling probability of the condensate atoms to the other potential well is half. However, when the system is periodically scanned in the adiabatic process, we find an interesting phenomenon. A small change in the cycle period can lead to the condensate atoms returning to the right well or tunneling to the left well. The system comes from a linear eigenstate back to a nonlinear one, which is completely different from the linear eigenstate evolution. We explain the results by using the energy level and the phase diagram.     

The interaction of an atom with a sub-Poissonian single field mode

The resonant interaction of a single atom with a single quantized field mode characterized by sub-Poissonian statistics is compared with its interaction with a coherent field mode. Two models are considered: the Jaynes-Cummings model (JCM) and the Raman-coupled model (RCM). Quadrature squeezing variances and photon number uncertainties are evaluated. In the JCM, sub-Poissonian field statistics lead to longer collapse times and more complete revivals than Poissonian statistics. In the RCM, which is characterized by periodic collapses and revivals, the collapse time is longer for sub-Poissonian fields.This work was supported in part by the UK Science and Engineering Research Council.     

Long range and temperature-dependent interaction between an alkali atom and a metallic surface; application to surface ionization

For explaining some long range and temperature dependent charge transfer involved in surface processes dealing with particles leaving a surface, we extend the usual chemisorption theory to larger distances. Treating the interaction of an alkali atom (lithium and sodium) on a metal surface (rhenium) in the chemisorption model, we introduce the temperature in the expression for the effective charges of the adsorbed atom. These effective charges are shown to be very sensitive to the temperature for atom-surface distances larger than 5 Bohr radii. The Coulomb repulsion effect between opposite spin electrons on the adsorbed particle allows us to describe the effective charges of both the positive and negative adsorbed ions. We apply our treatment to the positive surface ionization of thermal particles and give a new expression of the degree of ionization which asymptotically tends to the values of the Saha-Langmuir law. We found that the surface ionization process occurs at distances slightly decreasing with increasing temperatures, which are of the order of 13 Bohr radii for lithium on rhenium and of 15 Bohr radii for sodium on rhenium.     

波瓣波导谐振腔太赫兹回旋管的研究

以电子回旋脉塞非线性理论为基础, 结合三维电磁仿真软件, 通过导入高频场数值解替代理论解析的方法, 对波瓣波导谐振腔高次谐波太赫兹回旋管进行了理论和模拟研究. 给出了该类回旋管的起振电流、耦合系数以及注波互作用效率等重要参数, 并在此基础上设计了一只工作频率为0.4 THz, 工作模式TE₃₃模三次谐波波瓣波导谐振腔回旋管, 其电子注参数为1.0 A, 40.5 kV, 横纵速度比1.5,互作用区引导磁场为5.09 T, 输出功率达到3.3 kW.     

Inelastic processes in the interaction of an atom with an ultrashort electromagnetic pulse

Electron transitions occurring during the interaction of a heavy relativistic atom with a spatially inhomogeneous ultrashort electromagnetic pulse are considered by solving the Dirac equation. The corresponding transition probabilities are expressed in terms of known inelastic atomic form factors, which are widely used in the theory of relativistic collisions between charged particles and atoms. By way of example, the inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-like atoms are considered. The probabilities of ionization and production of a bound-free electron-positron pair on a bare nucleus, which are accompanied by the formation of a hydrogen-like atom in the final state and a positron in the continuum, are calculated. The developed technique makes it possible to take into account exactly not only the spatial inhomogeneity of an ultrashort electromagnetic pulse, but also the magnetic interaction.     

Three-body interaction between an atom and a monolayer film

An atom (B) situated near a plane of atoms (A) experiences an interaction potential energy V = (V₂ + V₃ + … The leading term is the sum over the monlayer of 2-body interactions. We compute here the 3-body correction V₃. Numerical results are presented for the case of noble gases, H and CH₄. For H or He near a Xe layer, V₃ reduces the well depth by ~ 10%.     

势阱中玻色-爱因斯坦凝聚气体的势场有效性和粒子数极限判据

基于最小动量态上的玻色-爱因斯坦凝聚(简称BEC)，给出了指数吸引势场中超冷玻色原子气体的势场有效性和势阱中所装载的原子数目极限判据.此判据给出了当所装载的原子数确定时，所需要的势场强度；或势场给定时，所装载的原子数目的极限. 关键词： 玻色-爱因斯坦凝聚 临界温度 最小动量态     

Kerr介质中纠缠原子与非简并双光子相互作用的动力学

考虑了在位于充满Kerr介质的腔中,一对纠缠的二能级原子之一与非简并双光子的相互作用,当该原子离开腔被作选测性测量时,分析测量后光场的量子性质,研究结果表明,在纠缠度一定时,Kerr效应使光场平均光子数的崩塌回复周期减小,光场的二阶相干度减弱,使Cauchy-Schwartz不等式关联程度减弱.     

Equation for the effective potential of an atom with the oscillation correction

The equation for the effective potential of an atom in the Thomas-Fermi model is considered. An equation is obtained for the oscillation correction to the potential, due to the nonanalytic dependence of the electron density on Planck's constant . The equation for the exchange and quantum corrections to the potential within the framework of the approximations discussed agrees with the equation of Kompaneets and Pavlovskii. The exchange, quantum, and oscillation corrections to the radial density of the atomic electrons are compared.The author wishes to thank L. Ya. Kobelev for his constant help and encouragement.