Electron momentum density and Compton profile by a semi-empirical approach

Here we propose a semi-empirical approach to describe with good accuracy the electron momentum densities and Compton profiles for a wide range of pure crystalline metals. In the present approach, we use an experimental Compton profile to fit an analytical expression for the momentum densities of the valence electrons. This expression is similar to a Fermi–Dirac distribution function with two parameters, one of which coincides with the ground state kinetic energy of the free-electron gas and the other resembles the electron–electron interaction energy. In the proposed scheme conduction electrons are neither completely free nor completely bound to the atomic nucleus. This procedure allows us to include correlation effects.We tested the approach for all metals with Z=3–50 and showed the results for three representative elements: Li, Be and Al from high-resolution experiments.     

Electron-phonon interaction and damping of phonons in simple metals application to aluminum

The theory of the electron-phonon interaction and of its influence on the damping of phonons is presented. The basic quantity entering into the theory, the matrix element of the effective electron-phonon interaction, will be obtained from an integral equation which is derived without making any simplifying assumptions about the wave functions and the energy spectrum of the Bloch electrons. Also for the matrix element of the ion-electron interaction a formula is given which allows an extension of the present calculation to metals with a complicated band structure. For the purpose of numerical computation in the metal Al the phonon lifetimes are determined in the free-electron model. The calculated values are compared with the experimental data of Nilsson and Stedman and with the theoretical results of Björkmanet al.     

EXCHANGE COUPLING BETWEEN TWO MAGNETIZED LAYERS IN A METAL

The exchange coupling energy for two magnetized monolayers embedded symmetrically in a metal and polarized in an arbitrary direction has been investigated in contact interaction approximation. Since the model can be solved exactly in particular for free-electron case, the coupling energy contributed from both extended state electrons and bound state electrons is calculated rigorously. For weak interaction, it is found that the leading term in the power-series expansion of density of states can give a correct coupling energy compared with rigorous one while extended state electrons give a much larger coupling energy. Furthermore, the relevant problems such as phase shift, 90°coupling and lattice effects have been discussed; an asymptotic expression of the interlayer coupling has been derived in a different way and used to calculate the exchange energy between magnetic layers in copper with Fermi surface obtained from de Haas-van Alphen effect.     

Quantum molecular dynamics of partially ionized plasmas

We study a partially ionized hydrogen plasma by means of quantum molecular dynamics, which is based on wave packets. We introduce a new model which distinguishes between free and bound electrons. The free electrons are modelled as Gaussian wave packets with fixed width. For the bound states the 1s-wave function of the hydrogen atom is assumed. In our simulations we obtain thermodynamic properties in the equilibrium such as the internal energy and the degree of ionization. The degree of ionization is in good agreement with theoretical predictions. The thermodynamic functions agree well with results from quantum statistics for 10000 K ≲ T ≲ 40000 K.     

Spin-dependent electron dynamics and recombination in GaAs<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys at room temperature

Conduction-electron spin polarization dynamics achieved by pulsed optical pumping at room temperature in GaAs_1−x N _x alloys with a small nitrogen content (x = 2.1, 2.7, and 3.4%) is studied both experimentally and theoretically. It is found that the photoluminescence circular polarization determined by the mean spin of free electrons reaches 40–45% and this giant value persists within 2 ns. Simultaneously, the total free-electron spin decays rapidly with the characteristic time ≈ 150 ps. The results are explained by spin-dependent capture of free conduction electrons on deep paramagnetic centers resulting in the dynamical polarization of bound electrons. A nonlinear theory of spin dynamics in the coupled system of spin-polarized free and localized carriers has been developed which describes the experimental dependencies, in particular, the electron spin quantum beats observed in a transverse magnetic field. The text was submitted by the authors in English.     

Dielectronic recombination rates for ions of the magnesium sequence—II

The dielectronic recombination (DR) rate coefficient α^DR is explicitly calculated for Ar, Fe and Mo target ions of the Mg isoelectronic sequence (12 electrons). The 2p transitions are dominant at high temperatures and are considered in detail with full LS coupling. This work extends our previous study in which both the 3s, Δn = 0 and 3s, Δn ≠ 0 transitions are considered. Scaling of α^DR with free-electron temperature is also discussed.     

Calculation of the electrical resistivity and the thermoelectric power of vacancies in copper and gold

The change of the electrical resistivity and of the thermoelectric power caused by vacancies in copper and gold was calculated. The effective scattering cross-section and its dependence on the energy of electrons was calculated in the free-electron approximation using the partial wave method. The scattering potential associated with a vacancy was approximated by a square barrier or by a screened Coulomb potential. The experimental value of the electrical resistivity is in good agreement with the value calculated in the free-electron approximation but the thermoelectric power differs appreciably from the free-electron value. Using an experimentally determined term, which depends on the shape of the Fermi surface, agreement with experiment was obtained.The author wishes to express his gratitude to Miss H. echová for programming and performing the calculations on the LGP 30 computer.     

Generation of Coherent X-ray Harmonic Radiation in a Single-Pass Free-Electron Laser with Phase Shift of Electrons Relative to Photons

Technical Physics - Evolution of bunching and harmonic power is theoretically studied for a single-pass free-electron laser (FEL) in which electrons are periodically phase-shifted relative to...     

Electron-beam conditioning by thomson scattering

A method is proposed for conditioning electron beams via Thomson scattering. The conditioning provides a quadratic correlation between the electron energy deviation and the betatron amplitude of the electrons, which results in enhanced gain in free-electron lasers. Quantum effects imply conditioning must occur at high laser fluence and moderate electron energy. Conditioning of x-ray free-electron lasers should be achievable with present laser technology, leading to significant size and cost reductions of these large-scale facilities.     

空间电荷场对自由电子激光中电子稳态轨道的影响

本文从三维模型出发,详细地研究了自由电子激光中电子束空间电荷场对相对论性电子稳态轨道的影响,发现考虑空间电荷场的三维效应后,电子稳态轨道出现新的不稳定性区域。 关键词：     

Cyclotron resonance studies on bulk and two-dimensional conduction electrons in InSe

Cyclotron resonance is reported for both bulk electrons and electrons bound to charged defect planes in the layer compound InSe. At temperatures below 20 K all carriers present are bound to defect planes and behave as two-dimensional accumulation layers. At higher temperatures the electrons are excited into bulk regions between the defects, and show three-dimensional, bulk behaviour. The conduction band is shown to exhibit an “anomalous anisotropy” with m_∥ = 0.08m₀ and m_⊥ = 0.14m₀. The bound, two-dimensional carriers exhibit a strong non-parabolicity, and show a band edge mass m_⊥ = 0.13 which is considerably lower than the bulk value possibly due to a reduction in the polaron constant in the degenerate electron gas.     

Interaction of dielectrics with femtosecond laser pulses: application of kinetic approach and multiple rate equation

We calculate the transient free-electron density in laser-irradiated dielectrics with two different approaches, both considering the energy distribution of excited electrons. The kinetic approach solves a system of complete Boltzmann collision integrals describing different excitation and relaxation processes in detail. The multiple rate equation (MRE) is an approximative way to keep track of the energy distribution of excited electrons with reduced numerical effort. Both methods are applied to trace dielectric breakdown, considering the changing optical parameters during irradiation with a high-intensity laser pulse. In the MRE approach we include also fast recombination, leading to a delay of the increase of the electronic density and to a decrease of the maximum number of free electrons.     

Effect of Initial Pitch-Angle of Electrons on Output Power of Free-Electron Laser with a Reversed Guide Magnetic Field

A nonlinear simulation is presented to the output power of the MIT free-electron laser experiment, which is in agreement with the measured data. It is found that the initial pitch-angle of the electrons substantially influences the output power and should be optimized carefully.     

Reply to “comment on ‘electromagnetic momentum in static fields and the Abraham-Minkowski controversy’”

We apply our method for testing the existence of a many-body bound state to two electrons in 2D, orbiting about an attractive center but repelling each other. We find the break-up boundary, on which this three-body state is unstable against ionization of one of the electrons. The result is significantly different in 2D than our earlier result in 1D. We show why this method is exact in dimensions d ? 2, but yields merely an upper bound for d > 2.     

Polaronic excitations in the doped polyacene

The polyacene as two coupled chains of transpolyacetylene has been studied based on an extended SSHHubbard model. The dimerized displacement u ₀ is found to be similar to the case of trans-polyacetylene, and equals to 0.04 Å. The energy-band gap is 0.38 eV, in agreement with other authors. In particular, we have considered some cases where polyacene is doped with one and two donor electrons. In the case of doping with one electron, a polaron spreading over two chains has been found; in the case of doping with two electrons having different spins, a stable bipolaron has been obtained, which is different from the one of transpolyacetylene; in the case of doping with two electrons having the same spins, two stable polarons which spread over two chains have been found. The bound electronic states corresponding to these cases are obtained.     

具有可变摆动器的自由电子激光器的一维数值计算

本文介绍了进行具有可变摆动器的自由电子激光器一维数值计算所使用的物理模型和一个激光放大器的具体计算例子。计算了摆动器参数、电子束和激光场之间的能量转换效率、激光强度、电子的相空间分布和能谱。得到的同步振荡周期和激光的饱和值与估计的值相符合。     

Orientation-dependent transparency of metallic interfaces

As devices are reduced in size, interfaces start to dominate electrical transport, making it essential to be able to describe reliably how they transmit and reflect electrons. For a number of nearly perfectly lattice-matched materials, we calculate from first principles the dependence of the interface transparency on the crystal orientation. Quite remarkably, the largest anisotropy is predicted for interfaces between the prototype free-electron materials silver and aluminum, for which a massive factor of 2 difference between (111) and (001) interfaces is found.     

Anti-resonance and the “0.7 anomaly” in conductance through a quantum point contact

We investigate the transmission of electrons through a quantum point contact by using a quasi-one-dimensional model with an extra local bound state staying below the band bottom. While the complete transmission in lower channels gives rise to plateaus of conductance at multiples of 2e²/h, the electrons in the lowest channel are scattered by the local bound state when it is singly occupied. This scattering produces a wide anti-resonant zero-transmittance for singlet formed by tunneling and local electrons, and has no effect on triplets, leading to an exact 0.75(2e²/h) shoulder prior to the first 2e²/h plateau. While at low temperature, the formation of Kondo cloud screens magnetic moment of the local bound state and reduces the scattering to the singlet channel, complementing the shoulder from 0.75 to 1.     

Spin polarized tunneling at finite bias

A mesoscopic spin valve is used to determine the dynamic spin polarization of electrons tunneling out of and into ferromagnetic (FM) transition metals at finite voltages. The dynamic polarization of electrons tunneling out of the FM slowly decreases with increasing bias but drops faster and even inverts with voltage when electrons tunnel into it. A free-electron model shows that in the former case electrons originate near the Fermi level of the FM with large polarization whereas in the latter, electrons tunnel into hot electron states for which the polarization is significantly reduced. The change in sign is ascribed to the matching of the electron wave function inside and outside the tunnel barrier.     

常参数波荡器自由电子激光中电子相轨道从周期性到非周期性的演化

本文讨论常参数波荡器(untapered wiggler)自由电子激光中电子的运动,发现考虑电子束与激光场之间的能量交换后,随着电子束等离子体频率增加,部份电子的相轨道将变成非周期性,随机型。 关键词：