Temperature dependence of magnetophonon resistance oscillations in GaAs/AlAs heterostructures at high filling factors

The temperature dependence of the magnetic-field resistance oscillations induced by acoustic phonons in a 2D system with a moderate mobility and a high electron density in the range T = 7.4–25.4 K has been studied. It has been established that the amplitude of the magnetophonon resistance oscillations in the system under study is determined by the quantum lifetime modified by the electron-electron scattering, in accordance with the results recently obtained in a GaAs/AlGaAs heterostructure with an ultrahigh mobility and a low electron density [A. T. Hatke et al., Phys. Rev. Lett. 102, 086808 (2009)]. The shift of the main maximum of the magnetophonon resistance oscillations to higher magnetic fields with increasing temperature is observed.     

Competing conduction mechanisms of two-dimensional electrons and bulk-like electrons in the n-type surface of the naturally oxidized p-type HgCdTe thin film

The surface transport properties of naturally oxidized p-type Hg_0.776Cd_0.224Te thin film were investigated in the magnetic-field region 0–14 T and in the temperature region 8–300 K. The Hall electron concentration increases with temperature, while the surface concentration of the two-dimensional electrons in the naturally oxidized surface, calculated by Shubnikov–de Haas oscillations, decreases as temperature increases at temperatures below 20 K. The contradiction and the extraordinary quantum Hall filling factors are accounted for by assuming extra bulk-like electrons in the surface region, which dominate the surface transport properties at temperatures over 8 K.     

Influence of the beam-forming conditions on the development of space-charge oscillations in a long-pulse relativistic electron beam

The characteristics of the space-charge oscillations of a long-pulse relativistic electron beam in magnetically insulated diodes are determined for different geometries of the electron acceleration section and for explosive-emission cathodes of different materials. The important role of the stream of electrons having high transverse velocities in the evolution of the oscillations is demonstrated, and the laws governing the generation of this stream are determined. Possible mechanisms of the space-charge oscillations are described, taking into account the interaction of the electron stream in the beam halo with the main electron stream, the development of diocotron instability in the stream of electrons emitted by the outer lateral surface of the plasma emitter, and the instability of the space charge of “long-lived” electrons in the beam transport channel. Zh. Tekh. Fiz. 68, 102–106 (April 1998)     

On some electromagnetic phenomena in the tether magnetoplasma cloud

Summary The tethered satellite system (TSS) will be accompanied by a variety of electromagnetic phenomena. An independent interconnected formation, a ?tethered magnetoplasma cloud? (TMC), moving in space along the orbit of TSS, at an altitude of about 300 km, will be created. This time-dependent cloud will be a very complicated inhomogeneous formation including electromagnetic oscillations and waves of different type. Some of these waves will be observed on the Earth's surface. Rarefiel regions of the magnetoplasma behind, and dense regions in front of the shuttle orbiter (SO) and the subsatellite (SS) will arise. The neutral nitrogen beam ejected by the thruster becomes an ion beam on the day-light part of the orbit. Its energy is much greater than the local thermal energy. Instabilities of different kind as well as diffusion and recombination effects are expected to accompany the interaction of these beams with the surrounding plasma. The electron beams will produce other types of instabilities. By the electrons precessing along the magnetic-field lines, a current (5·10³V, 0.5 A) should be induced in the 20th km length conducting tether. It will be closed at the bottom of the ionosphere. This huge magnetic loop, so-called ?phantom loop? (PL), should accompany the tether system along its orbit. The length of this ?tether electromagnetic tail? (TEMT) is about 200 km, its magnetic moment will be about 10¹³ A·cm². Alfvén waves and nonlinear effects of heating type may be produced by this loop along the magnetic-field lines. ?Strings? of hot plasma may accompany the tether system.     

Manifestation of exitonic effects in the magneto-oscillations of the intensity of the recombination radiation of 2D electrons

A study is made of the temperature dependence of the magnetooscillations of the recombination radiation of 2D electrons from the photoexcited size-quantization subband in an isolated GaAs/AlGaAs quantum well. It is shown that at high temperatures (T>10 K) the period of the oscillations is determined by the ratio of the intersubband energy splitting and the sum of the electron and hole cyclotron energies. It is found that as the temperature decreases (T<5 K), a new series of oscillations (with the same period but with a larger phase shift), which are associated with the appearance of excitonic states under the Landau levels, appears. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 10, 719–724 (25 November 1996)     

Liquid-crystal diode generator of low-frequency oscillations

The excitation of rhythmic current oscillations in a diode cell containing a nematic liquid crystal is studied. The external electric field in the interelectrode gap is directed parallel to the surfaces which orient the liquid crystal molecules. The current oscillations are accompanied by the formation of an autosoliton at the cathode, which propagates and disappears at the anode. A hypothetical model is proposed to explain this current instability. Zh. Tekh. Fiz. 68, 125–127 (January 1998)     

Influence of magnetic quantization on the effective electron mass in Kane-type semiconductors

Summary We study the effective electron mass at the Fermi level in Kane-type semiconductors on the basis of fourth order in effective mass theory and taking into account the interactions of the conduction electrons, heavy holes, light holes and split-off holes, respectively. The results obtained are then compared to those derived on the basis of the well-known three-band Kane model. It is found, takingn-Hg_1−x Cd _x Te as an example, that the effective electron mass at the Fermi level in accordance with fourth-order model depends on the Fermi energy, magnetic quantum number and the electron spin respectively due to the influence of band nonparabolicity only. The dependence of effective mass on electron spin is due to spin-orbit splitting parameter of the valence band in three-band Kane model and the Fermi energy due to band nonparabolicity in two-band Kane model. The same mass exhibits an oscillatory magnetic-field dependence for all the band models as expected since the origin of oscillations in the effective mass in nonparabolic compounds is the same as that of the Shubnikov-de Hass oscillations. In addition, the corresponding results for parabolic energy bands have been obtained from the generalized expressions under certain limiting conditions.     

On the degradation of ZnS:Cu,Al,Au phosphor powder: The effects of temperature

Abstract

The effects of temperature are discussed when the ZnS:Cu,Al,Au (P22G) phosphor powder is bombarded by a 2 keV electron beam with a current density of 88 mA/cm² at an oxygen pressure of 2 × 10^?6 Torr at temperatures between 25 and 300°C. The rate of surface reaction decreases at higher temperatures due to the reduction in the mean stay time of the O₂ on the surface which is vital for the reactions according to an electron stimulated surface chemical reaction model. A direct correlation between the temperature and the initial cathodoluminescence (CL) brightness which depicts thermal quenching of the CL was observed.     

Magnetic-field dependent intensity oscillations of the EHD luminescence in pure germanium

The magnetic-field dependence of the EHD luminescence in pure germanium is investigated using pulsed laser excitation. Intensity oscillations are found which vary with the delay time of the detection. A fit to a reaction-kinetic model yields a quantum efficiency of Q ≈ 25%. The main nonradiative process in the electron-hole liquid is found to be the Auger-recombination.     

Bound states of an electron in an impurity potential on the surface of liquid helium

The energies and widths of the levels of an electron on impurity centers on the surface of liquid helium are calculated with allowance for the deformation of the surface. The level shift associated with the deformation effects is small and decreases very slowly with increasing level number. However, even a small shift of the energy levels relative to one another affects ripplon scattering, which makes the main contribution to the level width at low temperatures. It is predicted theoretically that this width depends very strongly on the external parameters and on the level number and that a maximum obtains at a clamping field E _⊥=51500 V/cm. The width of the levels of an electron in a bound state is found to be less than for free electrons. This makes it possible to perform a beautiful spectroscopic experiment. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 9, 599–604 (10 November 1997)     

Nanoviscosity effect on the spin chemistry of an electron donor/Pt-complex /electron acceptor triad - classical and quantum kinetics interpretation

The magnetic-field dependent charge recombination kinetics upon ns-laser flash photolysis of a novel triarylamine/cyclometalated platinum complex/napthalenediimide triad (DPtA) have been measured in tetrahydrofuran (THF) and polytetrahydrofuran (pTHF) to study the spinchemical effect of a large increase of the macroviscosity of the solvent by a factor of about 1000. The magnetic-field dependence of the decay kinetics of the charge separated state has been accurately reproduced by a classical kinetic model, wherein the rate constants of transitions between spin substates of different Zeeman energy are represented by a single magnetic-field dependent rate constant k_±. In THF, the magnetic-field dependence of k_± is given by a double Lorentzian function which, in a double log plot, shows two characteristic steps that can be consistently assigned to the magnetic field inhibition of the coherent and incoherent i.e. relaxational spin mixing mechanism. In pTHF, the magnetic field effect on k_± is a single step function decreasing to its limiting value at about 5 times lower fields than in THF. As shown by a quantum theoretical simulation, in this solvent coherent and incoherent processes are contributing equally at all fields. The nanoviscosity of pTHF appears to be much smaller than its macroviscosity.     

Spectrum of polariton excitations of a two-dimensional electron plasma in a magnetic field

Polariton excitations associated with magnetoplasma and cyclotron oscillations in a two-dimensional (2D) electron plasma are studied. In contrast to previous works by other authors, it is concluded that there exists a low-frequency nontransmission band in the spectrum of 2D surface magnetoplasma polaritons. Radiative polariton excitations associated with nonuniform cyclotron oscillations of electrons in a 2D system are investigated. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 200–204 (10 August 1998)     

Charge-density-wave instabilities and quantum transport in the monophosphate tungsten bronzes with m = 5 alternate structure

Resistivity, thermoelectric power and magnetotransport measurements have been performed on single crystals of the quasi two-dimensional monophosphate tungsten bronzes (PO₂)₄(WO₃)_2m for m =5 with alternate structure, between 0.4 K and 500 K, in magnetic fields of up to 36 T. These compounds show one charge density instability (CDW) at 160 K and a possible second one at 30 K. Large positive magnetoresistance in the CDW state is observed. The anisotropic Shubnikov-de Haas and de Haas-van Alphen oscillations detected at low temperatures are attributed to the existence of small electron and hole pockets left by the CDW gap openings. Angular dependent magnetoresistance oscillations (AMRO) have been found at temperatures below 30 K. The results are discussed in terms of a weakly corrugated cylindrical Fermi surface. They are shown to be consistent with a change of the Fermi surface below 30 K. Received 23 November 1999 and Received in final form 23 March 2000     

Angular dependence of the giant magnetoresistance for a current perpendicular to the plane of the layers in a magnetic sandwich

A quantum-statistical model using the Kubo formalism is proposed for describing the magnetoresistance of a multilayer structure with the current perpendicular to the plane of the layers. In particular, this model describes the case of noncollinear magnetization of consecutive ferromagnetic layers of the structure. Interference between electron wave functions with different directions of the spin projections onto the magnetization axis, which arises in the noncollinear configuration, is investigated along with the role of electron scattering, not only within the bulk of the layers, but also at their interfaces. Fiz. Tverd. Tela (St. Petersburg) 41, 1814–1818 (October 1999)     

Effects of inhomogeneous magnetic fields on the electron transport through a quantum-wire system

The electron transport through a quantum-wire system in the presence of inhomogeneous magnetic fields is investigated theoretically. The system consists of two parallel quantum wires coupled by two ballistic windows, while the magnetic fields applied are uniform and equal in the two wires but vanishing in the two coupling windows and everywhere between the wires. Various transmissions of the system are calculated. It is found that the inhomogeneous magnetic fields induce irregular transmission oscillations in the low and moderate magnetic-field regions, and regular ones in the high field region. These transmission oscillations are due to interference between the electron waves traveling through different coupling windows and can be interpreted in terms of a semiclassical model. The Hall resistance of the system is also calculated and is found to show similar regular oscillations at high magnetic fields.     

Electron-optical phase shift of magnetic nanoparticles I. Basic concepts

The electron-optical phase shift induced in the electron beam due to the interaction with the electromagnetic field of magnetized nanoparticles of defined shape and arbitrary dimensions is calculated, presented and discussed. Together with the computable knowledge of vector potential and magnetic induction, including the demagnetizing field, and with the extension to more realistic geometries which will be presented in part II, this theoretical framework can be employed for the interpretation of transmission electron microscopy experiments on magnetic particles on the nanometre scale.     

Effect of deformation on spin splitting in quasi-2D hole systems

The effective Hamiltonian for holes in a 2D channel with in-plane uniaxial deformation is obtained. Two-dimensional channels on a Si surface are studied in the approximation of a spherically symmetric valence band and on the (100) and (110) surfaces taking account of the cubic symmetry. It is shown that the shift of the positions of the beats of the Shubnikov-de Haas oscillations that is linear in the deformation is due to the nonequivalence of the compression-tension axis and the direction perpendicular to it in the plane on the (110) surface. Fiz. Tverd. Tela (St. Petersburg) 40, 546–549 (March 1998)     

Underestimating the width of the bandgap in the electronic spectra of La2CuO4

It is shown that the width of the bandgap determined by the simultaneous analysis of the experimental photoelectron and inverse photoemission spectra of the surface of La₂CuO₄ using a common energy scale is underestimated by 1 eV. The electronic and satellite structures of the spectra of La₂CuO₄ are calculated on the basis of the multiband p-d model and the sudden perturbation approximation. It is shown that shakedown processes shift the one-electron contour of the final two-hole configuration of the photoelectron spectrum 1 eV down the energy scale and shift the contour of the final d ¹⁰ configuration of the inverse photoemission spectrum downward by 2 eV; these shifts cause the energy splitting between the filled and empty bands to be underestimated. Fiz. Tverd. Tela (St. Petersburg) 39, 449–451 (March 1997)     

Signature of the electron-electron interaction in the magnetic-field dependence of nonlinear I-V characteristics in mesoscopic systems

We show that the nonlinear I-V characteristics of mesoscopic samples with metallic conductivity should contain parts which are linear in the magnetic-field and quadratic in the electric field. These contributions to the current are entirely due to the electron-electron interaction and consequently they are proportional to the electron-electron interaction constant. We also note that both the amplitude and the sign of the nonlinear part of the current exhibit random oscillations as a function of temperature.