Coulomb drag in the quantum Hall state: Role of disorder

We consider Coulomb drag between two layers of two-dimensional electron gases subject to a strong magnetic field, with the Landau level filling factor in each layer being . We find to be very large, as compared to the zero magnetic field case. We attribute this enhancement to the slow decay of density fluctuations in a strong magnetic field. For a clean system, the linear -dependence of the longitudinal conductivity, characteristic of the state, leads a unique temperature dependence – . Within a semiclassical approximation, disorder leads to a decrease of the transresistivity as compared to the clean case, and a temperature dependence of at low temperatures.     

开放量子台球体系散射的赝路径半经典近似

本文讨论正方形量子台球的输运性质,考虑电子以费米能量穿过台球区域,在台球出口和入口处对入射和出射波函数采用基尔霍夫散射.采用微扰论的Dyson方程得到半经典格林函数,并把赝路径半经典近似作微扰展开得到体系的传输矩阵元.比较了传输矩阵元的傅立叶变换谱的峰位置与腔内自由电子经典轨道长度,发现在精度允许范围内它们符合的很好.     

开放量子台球体系散射的赝路径半经典近似

本文讨论正方形量子台球的输运性质，考虑电子以费米能量穿过台球区域，在台球出口和入口处对入射和出射波函数采用基尔霍夫散射．采用微扰论的Dyson方程得到半经典格林函数，并把赝路径半经典近似作微扰展开得到体系的传输矩阵元．比较了传输矩阵元的傅立叶变换谱的峰位置与腔内自由电子经典轨道长度，发现在精度允许范围内它们符合的很好．     

Quantum-Mechanical Description of the Electromagnetic Interaction of Relativistic Particles with Electric and Magnetic Dipole Moments

The Hamiltonian of relativistic particles with electric and magnetic dipole moments that interact with an electromagnetic field is determined in the Foldy-Wouthuysen representation. Transition to the semiclassical approximation is carried out. The quantum-mechanical and semiclassical equations of spin motion are derived. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 9–12, August, 2005.     

Excitation of surface plasmons by electrons in a parabolic beam

A theory is presented for the excitation of surface plasmons by an electron beam following a non-touching path above a metal surface in Born approximation. The metal is assumed to possess only surface plasmon excitations. Configurations involving deflection of the electron beam in a parallel plate condensor, and by scattering from a field emission tip are envisaged. The relation between experimental conditions and the validity of the semiclassical approximation is discussed. The region of space above the surface in which scattering occurs is calculated, but the feasability of the experiment depends on electron optical factors which are outlined.     

Weak and electromagnetic properties of hyperons in a semiclassical approximation

We discuss hyperon decays and hyperon magnetic moments using a chiral lagrangian where the baryons appear as solitons. Some relations are derived using the semiclassical approximation.     

Semiclassical theory of molecular collisions: Real and complex-valued classical trajectories for collinear atom Morse oscillator collisions

Real and complex-valued classical trajectories have been calculated for the collinear collision of an atom with a Morse oscillator. They are used in three semiclassical approximations for the transition probability: a Bessel uniform approximation, an Airy uniform approximation and a primitive semiclassical approximation. Comparison with exact quantum results shows that the Bessel uniform approximation is accurate even for near elastic collisions where the Airy and primitive approximations break down. The Airy and Bessel approximations agree quite closely for inelastic collisions however. The primitive semiclassical approximation is less accurate than either the Airy or Bessel approximation.     

Quantum-chaotic scattering effects in semiconductor microstructures

We show that classical chaotic scattering has experimentally measurable consequences for the quantum conductance of semiconductor microstructures. These include the existence of conductance fluctuations-a sensitivity of the conductance to either Fermi energy or magnetic field-and weak-localization-a change in the average conductance upon applying a magnetic field. We develop a semiclassical theory and present numerical results for these two effects in which we model the microstructures by billiards attached to leads. We find that the difference between chaotic and regular classical scattering produces a qualitative difference in the fluctuation spectrum and weak-localization lineshape of chaotic and nonchaotic structures. While the semiclassical theory within the diagonal approximation accounts well for the weak-localization lineshape and for the spectrum of the fluctuations, we uncover a surprising failure of the semiclassical diagonal-approximation theory in describing the magnitude of these quantum transport effects.     

Tight binding electrons on a disordered square lattice in a magnetic field

A semiclassical WKB treatment of the density of states spectrum of tight-binding electrons moving in a disordered two dimensional lattice in the presence of a transverse magnetic field is presented. The disorder is accounted for in the coherent potential approximation and analytical results are derived. For both ordered and disordered systems the line position of magnetic subbands as well as the cluster lineshape of the density of states agree quite well with exact numerical results.     

Long-range potentials and stark broadening of neutral lines

The influence of the dipole polarization and quadrupole potentials on the Stark broadening of isolated neutral lines in a plasma has been investigated within the semiclassical approximation. It has been shown that both the perturbing electron trajectories and the minimum impact parameter may undergo a noticeable change when reaction of the emitter on the impact electron is taken into account. The effects on the halfwidths of selected lines have been examined within the impact approximation. Calculated results are compared both with available experimental data and other theoretical results. The importance of including long-range effects is also discussed.     

2D chaotic quantum states in superlattices

The semiclassical motion of an electron along the axis of a superlattice may be calculated from the miniband dispersion curve. Under a weak electric field the electron executes Bloch oscillations which confines the motion along the superlattice axis. When a magnetic field, tilted with respect to the superlattice axis, is applied the electron orbits become chaotic. The onset of chaos is characterised by a complex mixed stable-chaotic phase space and an extension of the orbital trajectories along the superlattice axis. This delocalisation of the orbits is also reflected in the quantum eigenstates of the system some of which show well-defined patterns of high probability density whose shapes resemble certain semiclassical orbits. This suggests that the onset of chaos will be manifest in electron transport through a finite superlattice. We also propose that these phenomena may be observable in the motion of trapped ultra-cold atoms in an optically induced superlattice potential and magnetic quadrupole potential whose axis is tilted relative to the superlattice axis.     

On the semiclassical impulse approximation for electron capture in asymmetric ion-atom collisions

A derivation of the impulse approximation for the capture of a targetK-shell electron by a light projectile in ion-atom collisions is given in the framework of the semiclassical approximation. The impact-parameter dependence of the capture probability is calculated numerically without further approximations, and shows good agreement with recent experimental results for protons colliding with Ne and Ar. The validity of several peaking approximations and the relation to ionisation theories is briefly discussed.     

Calculated ionization cross sections for proton-fullerene ion collisions

A simple jellium model is constructed in order to obtain one-electron wave functions for the valence electrons of the fullerene. With this jellium wave function we have calculated ionization cross sections for proton-C₆₀ ⁺ collisions in the semiclassical approximation. For higher projectile velocities, for which the semiclassical approximation is valid also for electron impact, theoretical cross sections fit satisfactorily the experimental data of Völpel et al. [Phys. Rev. Lett. 71 (1993) 3439].     

Quantum adiabatic approximation to interacting boson-fermion systems

We present an adiabatic approximation method for the path integral of the Fermi field in the presence of a Bose field. The adiabatic phenomenon recently found by Berry and Simon is used for evaluating the Grassman path integral. Then we obtain the path integral of the effective action analogous to a magnetic field, and the quantization rule is derived by applying the semiclassical quantization method.     

Smearing of the two-dimensional Kohn anomaly in a nonquantizing magnetic field: implications for interaction effects

Thermodynamic and transport characteristics of a clean two-dimensional interacting electron gas are shown to be sensitive to the weak perpendicular magnetic field even at temperatures much higher than the cyclotron energy, when the quantum oscillations are completely washed out. We demonstrate this sensitivity for two interaction-related characteristics: electron lifetime and the tunnel density of states. The origin of the sensitivity is traced to the field-induced smearing of the Kohn anomaly; this smearing is the result of curving of the semiclassical electron trajectories in magnetic field.     

Influence of constant electric field on generation of higher harmonics in semiconductor carbon nanotubes

The generation of higher harmonics by semiconductor carbon nanotubes in the presence of constant electric field polarized along the nanotube axis is considered. The analysis is performed in the semiclassical model of electron motion without taking into account interband transitions. The electron system of carbon nanotubes is described using the kinetic Boltzmann equation in the relaxation time approximation. The dependence of higher harmonic amplitude on the field characteristics is studied.     

平行电磁场中H-光剥离电子轨道分岔现象的研究

当改变能量、位置或场强等参数时,电磁场中里德堡态的原子、分子和离子等体系将出现分岔现象,从而导致波函数在分岔点附近发散,半经典闭合轨道理论不再适用.本文分析并计算了平行电磁场中H-光剥离电子轨道的分岔现象,并采用统一近似的方法进行定域修正,从而消除了分岔点的奇异性,得到了合理的光剥离电子流的分布.     

Semiclassical description of reactions at energies near the Coulomb barrier

The modified semiclassical approximation of Coulomb matrix elements is extended to include effects of distorting nuclear potentials in the scattering wave functions. The applicability and efficiency of the proposed semiclassical method are discussed. The advantages of this approximation are shown for a typical heavy-ion transfer reaction.     

A Uniform Semiclassical Calculation of the Rings in Photodetachment Microscope

We describe a uniform semiclassical theory for the spatial distribution of the photodetached electron of H^- in the presence of a static electric field. In this theory we propagate the photodetached electron wavefunction using a mixed position and momentum coordinate method to large distance where a uniform approximation to the electron flux distribution is calculated. Details are given for the propagation of the mixed coordinate wavefunction with cylindric symmetry and the transformation between configuration space wavefunction and the mixed position and momentum wavefunction.