Magnetic exchange energy of two-dimensional electrons

The exchange energy of a two-dimensional electron gas was evaluated exactly in the presence of a magnetic field when only the lowest Landau level is occupied fractionally.     

Diffusion of electrons scattered by short-range impurities in a quantizing magnetic field

Formulas for transverse diffusion and conductivity in a semiconductor are obtained for electrons scattered by neutral impurities in a quantizing magnetic field. The formulas are valid for an impurity potential of arbitrary depth. Based on Kubo’s theory [1], calculations are performed using electron wavefunctions of the problem of single-impurity scattering in a magnetic field [2]. The poles of the scattering amplitude correctly determine electron eigenstates and magnetic impurity states. As a result, an exact expression is found for the dependence of transverse diffusion coefficient D _⊥ on longitudinal electron energy ? due to scattering by short-range (neutral) impurities. The behavior of D _⊥(?) is examined over an interval of magnetic field strength for several values of impurity potential depth. The experimental observability of diffusion and conductivity using IR lasers is discussed.     

Effect of spontaneous magnetic fields on energy transfer by fast electrons in spherical laser targets

It is shown that the spontaneous magnetic fields generated due to development of hydrodynamic instability in the process of compression of spherical laser targets can substantially affect the energy transfer by fast electrons. The analytical solutions to the kinetic equation for the distribution function of fast electrons are obtained taking into account the reflection from the region of the magnetic-field localization. On the basis of these solutions, the effect of the spontaneous magnetic fields on the specific energy released by the fast electrons per unit mass and on preheating of the target material being compressed is investigated.     

Electron energy relaxation in the presence of magnetic impurities

We study inelastic electron-electron scattering mediated by the exchange interaction of electrons with magnetic impurities and find the kernel of the corresponding two-particle collision integral. In a wide region of parameters, the kernel K is proportional to the inverse square of the transferred energy, K proportional to J4/E2. The exchange constant J is renormalized due to the Kondo effect. At small energy transfers, the 1/E2 divergence is cut off; the cutoff energy is determined by the dynamics of the impurity spins. The obtained results may provide a quantitative explanation of the experiments of Pothier et al. [Phys. Rev. Lett. 79, 3490 (1997)] on anomalously strong energy relaxation in short metallic wires.     

Strain enhanced exchange interaction between impurities in graphene

We study the effect of strain on the exchange interaction between two magnetic impurities in graphene. We calculate the exchange integrals between the impurities using a Green function technique. The calculation results indicate that strain may remarkably enhance the exchange interaction between the impurities within small distance. We explain the micromechanism of generating this phenomenon.     

Appearance of magnetic order for Cr impurities in exchange enhanced hosts

In systems like $\text{Pd;Ni}$ where the impurities have a high characteristic temperature in the dilute limit, most of the features traditionally associated with the appearance of magnetic order are absent. In such systems it has been demonstrated that a plot of Δ? (1.5K) – Δ? (4.2K) against concentration exhibits a peak at the critical concentration for ordering. We have used this technique to estimate this critical concentration at 5 at. % and 11 at. % Cr in Pd and Pt respectively.     

Effect of runaway electrons on the ionisation equilibria and radiation of Tokamak impurities

The results of calculations of the ionisation equilibria and radiative cooling of Tokamak impurities are given as a function of electron temperature. In the relevant rate coefficients, the Maxwellian distribution of electron energies has been assumed to be distorted by a runaway tail caused by the finite electric field in a Tokamak. In order to investigate the effect of runaways on the start-up phase of a Tokamak, non-steady-state calculations have also been performed.     

Effect of cyclotron resonance on the indirect exchange between localized magnetic moments

The effect of the simultaneous presence of an electromagnetic and a D.C. magnetic field on the magnon dispersion relation is discussed within the s-d-model. It is found that as the radiation frequency approaches the electron cyclotron frequency there is a quenching of the carrier contribution to the spin wave dispersion equation.     

引导磁场对收集极中电子能量沉积的影响

理论分析了引导磁场对收集极材料中电子运动的约束作用,推导了引导磁场作用下二次电子的逃逸条件,利用蒙特卡罗方法计算了引导磁场作用下电子束在收集极中的能量沉积规律。研究结果表明:引导磁场对电子在材料内部的运动约束作用很弱,对二次电子有强约束作用;大部分二次电子经拉莫回旋再次轰击在收集极上被收集,逃逸的二次电子沿引导磁场方向进入束波作用区;增大电子的入射角度时,束流密度的降低和二次电子的再次入射降低了收集极中电子的最大沉积能量密度,提高了收集极的耐电子轰击能力。     

Ground-state energy of two-dimensional interacting electrons in strong magnetic fields

Summary The ground-state energy of two-dimensional interacting electrons in a strong magnetic field in the angular-momentum representation is studied using a modified Lanczos diagnonalization method. In the presence of a positive background density the ground-state energy increases with the total angular momentum, while a cusp-type behaviour appears. The problem of the electron-impurities interaction is formulated as well. The results are discussed in connection with the observed fractional quantum Hall states. Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction. The author of this paper has agreed to not receive the proofs for correction.     

Binding energy between the magnetic impurity electron and the conduction electrons in the Anderson-Holstein model

A single-level Anderson-Holstein model is investigated using the Lang-Firsovtransformation followed by a zero-phonon averaging and the Kikuchi-Morita Clustervariation method as adopted by Bose and Tanaka in the case of Anderson model. The groundstate energy of the system at zero temperature and the binding energy between the magneticimpurity and the conduction electrons are calculated for the symmetric case ε _d = ?(U/2). Subsequently, the effect of the electron-phononinteraction on the ground state energy and the binding energy is investigated.     

Effect of exchange interaction on the spin fluctuations of localized electrons

A microscopic theory of spin fluctuations in an ensemble of electrons localized on donors in a bulk semiconductor has been developed. Both the hyperfine interaction of the electron spin with spins of host lattice nuclei and the exchange interaction between the electrons have been taken into account. A model of clusters to calculate spin noise spectra of the ensemble of localized charge carriers has been proposed. It has been shown that the electron-electron exchange interaction leads to an effective averaging of random nuclear fields and a shift of the peak in the spin-fluctuation spectrum towards lower frequencies.     

Mapping itinerant electrons around Kondo impurities

We investigate single Fe and Co atoms buried below a Cu(100) surface using low temperature scanning tunneling spectroscopy. By mapping the local density of states of the itinerant electrons at the surface, the Kondo resonance near the Fermi energy is analyzed. Probing bulk impurities in this well-defined scattering geometry allows separating the physics of the Kondo system and the measuring process. The line shape of the Kondo signature shows an oscillatory behavior as a function of depth of the impurity as well as a function of lateral distance. The oscillation period along the different directions reveals that the spectral function of the itinerant electrons is anisotropic.     

Magnetic exchange interactions in quantum dots containing electrons and magnetic ions

We present a theory of magnetic exchange interactions in quantum dots containing electrons and magnetic ions. We find the interaction between the electron and Mn ion to depend strongly on the number of electrons. It can be switched off for closed shell configurations and maximized for partially filled shells. However, unlike the total electron spin S which is maximized for half-filled shells, we predict the exchange interaction to be independent of the filling of the electronic shell. We show how this unusual effect manifests itself in quantum dot addition and excitation spectrum.     

Scattering theory of electrons on impurities in compensated semiconductors

In this paper we study the temperature behavior of the electron mobility in n-type compensated semiconductors, caused by scattering on neutral, ionized, and dipole impurity centers. With increased temperature, neutral impurity atoms and paired oppositely charged donor-acceptor dipole scattering impurity centers transform into separate ionic scattering centers. These transformations of scattering centers take place at various temperatures. We find that the mobility caused by electron scattering on separate impurity ions does not change with temperature monotonically — there appear two minima under certain conditions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 106–109, October, 1987.     

Scattering of conduction electrons by impurities in quantizing magnetic fields and calculation of electrical conductivity

The method of partial phases was used to obtain a formula for the electrical conductivity of conduction electrons scattered by impurities in quantizing magnetic fields for the case of an anisotropic carrier spectrum, when its isoenergetic surface is an ellipsoid of revolution, and the magnetic field is parallel to its major semiaxis. Equations for finding the phase shifts are given.Translated from Izvestiya Vysshikh Uchebynkh Zavedenii, Fizika, No. 2 pp. 98–102, February, 1978.In conclusion we thank Prof. A. Samoilovich and Docent S. L. Korolyuk for help in conducting this work.     

Effect of diamagnetic impurities on the magnetic susceptibility of iron borate

The low-frequency magnetic susceptibility of a FeBO₃ single crystal doped with diamagnetic Mg ions was measured by a magnetooptical method. It is shown that the introduction of Mg ions into the composition of this easy-plane weak ferromagnet results in the appearance, at low temperatures, of a strong in-plane magnetocrystalline anisotropy and also causes a marked difference between the field dependences of the magnetic susceptibility measured in magnetic fields applied along different directions in the basal plane of the crystal. The revealed specific features of the field dependence of the magnetic susceptibility of the crystal studied are associated with the transformation of its magnetic structure during magnetization.     

Free energy of a strong-coupling superconductor with magnetic impurities in Shiba-Rusinov approximation

We evaluate numerically the free energy of a strong-coupling superconductor with paramagnetic impurities in the model of Shiba and Rusinov. Our work is based on a recent formula for the free energy given by Yamamoto and Nagi. This formula is based on the same fundamental expression as used by Schossmann and Schachinger but without their simplfying approximations. Our results are numerically quite different from the previous ones. It is still concluded, however, that the thermodynamic critical field is very sensitive to the model chosen to describe the scattering.     

Effect of the dielectric-constant mismatch and magnetic field on the binding energy of hydrogenic impurities in a spherical quantum dot

Within the effective mass approximation and variational method the effect of dielectric constant mismatch between the size-quantized semiconductor sphere, coating and surrounding environment on impurity binding energy in both the absence and presence of a magnetic field is considered. The dependences of the binding energy of a hydrogenic on-center impurity on the sphere and coating radii, alloy concentration, dielectric-constant mismatch, and magnetic field intensity are found for the GaAs–Ga_1−xAl_xAs–AlAs (or vacuum) system.