Confined-acoustic-phonon-assisted cyclotron resonance via multi-photon absorption process in GaAs quantum well structure

Phonon-assisted cyclotron resonance (PACR) in GaAs quantum well (QW) structure is investigated via multi-photon absorption process when electrons interact with the confined acoustic phonon through deformation potential. The additional peaks in the absorption spectrum due to transitions between Landau levels accompanied with the emission and absorption of phonons are indicated. The dependence of absorption power on the temperature, magnetic field and well width is presented. Using profile method, we obtain PACR-linewidth as profiles of the curves. The temperature, magnetic field and well width dependences of the PACR-linewidth are investigated. The results are compared with those in the case of mono-photon absorption process, as well as in the electron-bulk acoustic phonon interaction. The results show that the multi-photon absorption process is strong enough to be detected in PACR.     

Cyclotron resonance for electrons over helium in a resonator

The cyclotron resonance (CR) problem for electrons over a helium film occupying the lower part of a resonator is solved. This problem is shown to represent an example of the well-known problem on the behavior of a system of coupled oscillators. For such oscillators, the coupling constant is determined as a function of the problem parameters with its minimal value in zero magnetic field and its maximal value at resonance conditions, when the cyclotron frequency coincides with one of the resonator modes. The details of the CR absorption of microwave energy by the coupled system formed by 2D electrons and a resonator are calculated. The results are discussed in application to the known CR experiments with electrons over helium.     

Cyclotron resonance study of conduction electrons in n-type indium antimonide under a strong magnetic field—II: Hot electrons

A system of hot electrons in the n-InSb under the application of a strong magnetic field has been studied by far IR cyclotron resonance. A three band model and an energy independent scattering time were assumed in analyzing the line shape variation with electric field applied either parallel or perpendicular to the magnetic field. Two kinds of electron temperature, inter- and intra-subband, were introduced to describe the electron distribution in energy space. The electron distribution function was found to deviate from an essentially Maxwellian form in the manner predicted by Yamada and Kurosawa. A remarkable difference exists between the two geometries: E∥H and E⊥U. A brief survey of cyclotron emission, and the reverse process of hot electron cyclotron absorption, is summarized at the end as an addendum.     

High-Energy Electron Production by Vp × B Acceleration in Microwave-Plasma Interaction Experiments

Detailed experimental observations on the microwave plasma interaction in a nonuniform plasma with weak magnetic field (?/? ? 10-2) have revealed that high-energy electrons are produced by a process of the VP × B acceleration, where ? and ? are, respectively, electron cyclotron and microwave frequencies. The maximum energy of hot electrons increases almost linearly to about 1 keV with the RF power up to 8 kW. Hot electrons are produced from typically two regions; one in the underdense region (several centimeters down the critical layer for the resonance absorption) and the other in the resonance absorption area. The theoretical predictions have interpreted the experimental results in reasonable agreement.     

Cyclotron resonance in the InAs/GaSb heterostructure in an inclined magnetic field

The mechanism of cyclotron resonance line splitting in the InAs/GaSb heterostructure in an inclined magnetic field has been studied experimentally and theoretically. It is shown that the admixing of electron and hole states leads to anticrossing of the Landau levels and, hence, to splitting of the cyclotron resonance line. In the case of an inclined magnetic field, the splitting is not observed, which is explained by the suppression of the admixing of electron and hole states due to the occurrence of an additional barrier for electrons and holes given a longitudinal magnetic field component.     

Nonlinear waves in bismuth

The propagation of short radio waves in a bismuth crystal in a constant magnetic field H aligned parallel to the bisecting axis oriented normally to the surface of the crystal plate is investigated theoretically. In this geometry, spatial inhomogeneity of the wave field has a weak effect on electrons and a strong effect on holes. It is demonstrated that, in a certain range of magnetic field strengths H, the bismuth crystal is characterized by two modes, namely, a helicon and a doppleron, whose damping is governed by cyclotron absorption of holes. For small amplitudes of the wave field in a linear regime, the damping lengths of both modes are relatively short due to cyclotron absorption. In a nonlinear regime, the magnetic field of the radio wave captures holes responsible for cyclotron absorption. As a result, the absorption is suppressed and the damping lengths of the helicon and the doppleron increase drastically. The excitation of these modes in the bismuth plate results in the fact that the dependence of the impedance of the plate on the magnetic field strength H exhibits resonance behavior and the transmittance of the plate increases by more than two orders of magnitude. It is shown that this effect should manifest itself at frequencies of the order of a few megahertzes in relatively weak magnetic fields (of the order of a few tens of oersteds).     

Doppler-shifted cyclotron resonance in tungsten plates with atomic pure surface

The surface resistance of thin monocrystalline W plates as a function of the constant magnetic field H directed along the normal to the sample surface is studied in the r.f. spectrum region. The sample surface was cleaned in high vaccum (10^-11 torr) or coated with the monomolecular impurity film. The oscillating with the magnetic field part R_osc due to the Doppler-shifted cyclotron resonance is studied. The doppleron oscillation amplitude is found to depend on the surface state and increases with the crystal cleaning. The observed changes are caused by the increase of the specular reflection coefficient for resonance electrons. With the deviation of the magnetic field from the normal to the plate surface, the doppleron wave undergoes a collisionless magnetic Landau damping and the signal amplitude decreases down to values comparable with that of Gantmakher-Kaner oscillations. Cleaning of the surface (and related increase of specularity) gives rise to a further decrease of the doppleron amplitude and appearance of additional interference maxima induced by the Gantmakher-Kaner effect.     

Cyclotron Resonance of an Interface Magnetopolaron at Finite Temperatures

Taking into account the interaction of an electron with both bulk longitudinal-optical (LO) and interface-optical (IO) phonons, the cyclotron resonance of an interface magnetopolaron at finite temperatures is investigated by using the generalized Larsen perturbation-theory method. It is shown that the absorption and emission resonance must be considered at the same time at finite temperatures. The results also show the important role played by the electron-IO phonon interaction. For the GaAa/GaSb structure, splitting of the cyclotron resonance spectrum and temperature dependence of the threefold splitting cyclotron resonance mass of the magnetopolaron in the resonant magnetic field region are studied.     

The absorption of rayleigh's sound waves in metals in a parallel magnetic field

The electron absorption coefficient has been calculated for the Rayleigh waves in a metal, with the magnetic field parallel to the boundary. Reflection of electrons from the metal surface is assumed to diffuse. For high magnetic fields the shape and width of the absorption lines have been investigated as well as maximum values of the attenuation. For low fields oscillations of the geometric and cyclotron resonance type are predicted.     

Spectroscopy of one-dimensional subbands on InSb

By means of high resolution optical lithography two-dimensional (2D) electron inversion layers in metal-oxide-semiconductor (MOS) structures on InSb are laterally confined to narrow channels. The widths of the channels (w≈100nm) are comparable to the de-Broglie wavelength of the electrons and formation of one-dimensional (1D) subbands results. This is verified by direct spectroscopy of intersubband transitions between the 1D subbands at far-infrared frequencies. Cyclotron resonance experiments also show the importance of the lateral confining potential. In particular, the transition from 1D to 2D electronic behavior is observed when the magnetic field strength is increased and the cyclotron radius ℓ becomes much less than the channel width w.     

Nonlinear doppler-shifted cyclotron resonance in aluminum

The Doppler-shifted cyclotron resonance in an aluminum plate in the geometry when constant magnetic field H is directed along the [100] crystallographic axis oriented normally to the surface of the plate is studied theoretically. The analysis is performed for a simple model Fermi surface possessing fourth-order symmetry. Capture of holes by the magnetic field of a radio-frequency wave is shown to considerably decrease the effectiveness of cyclotron absorption at large exciting field amplitudes. This suppresses the collisionless damping of dopplerons (propagating modes related to odd cyclotron resonance harmonics). As a result, the sample becomes more transparent to radio-frequency radiation.     

Nonlinear waves in zinc

A theoretical analysis is made of Doppler-shifted cyclotron resonance in zinc in linear and nonlinear regimes. It is shown that the absence of a threshold for cyclotron absorption by holes makes the doppleron strongly damped or eliminates it for low-amplitude wave-fields. At high amplitudes capture of holes by the magnetic field of the wave suppresses collisionless absorption and the doppleron can propagate. As a result, the impedance of the plate is an oscillating function of the magnetic field. It is shown that the effect should be observed at frequencies of the order of a few tens of kilohertz, in magnetic fields of the order of a few kilogauss, and for exciting field amplitudes of the order of a few tens of gauss. Zh. éksp. Teor. Fiz. 114, 725–734 (August 1998)     

Cyclotron resonance of electrons in localized surface states

The distribution of dipole strength is calculated for a system of electrons moving in a twodimensional surface subband in the presence of a magnetic field. At low densities, where an appreciable part of the electrons occupy localized states the cyclotron resonance exhibits a characteristic field and density dependent structure. The observed drop of the apparent cyclotron mass in Si (100) surfaces is described. The effective activation energy is calculated. From the mobility data in the activated conduction regime it is concluded that only about 20% of the localized states have a localization range of the order of 100 Å or less.     

Five-level k · p model for conduction electrons in GaAs. Description of cyclotron resonance experiments

Five-level k·p model for the conduction electrons in GaAs in the presence of a quantising magnetic field is developed and used to describe spin splittings of the cyclotron resonance and the donor-shifted cyclotron resonance peaks, observed in this material up to fields of 22.5 T. It is shown that the spin splittings are insensitive to polaron effects and that their values can be very well described by the model.Required band parameters correctly account for the rate of electron spin relaxation in GaAs due to inversion asymmetry, as determined by other authors.     

Cyclotron Resonance of a Magnetopolaron in a Quantum Well at Finite Temperatures

Taking into account the interaction of an electron with both bulk longitudinal-optical (BO) and surface-optical (SO) phonons, the cyclotron resonance of a magnetopolaron in a quantum well at finite temperatures is investigated by using the generalized Larsen perturbationtheory method. It is shown that the absorption and emission resonances must be considered at the same time at finite temperatures. The results also show that the electron-SO phonon interaction plays an important role as well as the electron-BO phonon interaction, especially when the quantum well width is getting thinner. For an experimentally interesting GaAs/Ga_1-xAl_xAs sandwich structure, the splitting of the cyclotron resonance spectrum and the temperature dependence of two splitting cyclotron resonance mass of the magnetopolaron in the resonant magnetic field region have been studied.     

Calculation of the cyclotron transition line-width by confined phonon scattering using the projection-reduction method

A formula to obtain the cyclotron transition line-widths for a system of electrons interacting with confined-acoustic phonons through the deformation potential in a quantum well is derived using the projection-reduction method. The result contains the distribution functions for the electrons and phonons properly. Therefore, the phonon absorption and emission processes can be explained in an organized manner and the result can be represented diagrammatically, through which insight into the quantum dynamics of electrons in a solid can be obtained. The formula is used to calculate the cyclotron transition line-widths in silicon. It is shown that the line-width increases with increasing temperature but the well width and magnetic field dependence of the line-width are complicated. It is also shown that only a few low-energy confined modes contribute significantly to the line-widths.     

Energy band model and properties of electrons in bismuth

A new energy band model for bismuth electrons is presented which gives very good fits to several experiments (de Haas-van Alphen effect, cyclotron resonance, magnetic surface resonance, radio-frequency size effect) and reasonably good fits to other properties (limiting-point cyclotron resonance, tilt effect) as function of the orientation of the magnetic field.     

Study of runaway electron behaviour during electron cyclotron resonance heating in the HL-2A Tokamak

During the current flat-top phase of electron cyclotron resonance heating discharges in the HL-2A Tokamak, the behaviour of runaway electrons has been studied by means of hard x-ray detectors and neutron diagnostics. During electron cyclotron resonance heating, it can be found that both hard x-ray radiation intensity and neutron emission flux fall rapidly to a very low level, which suggests that runaway electrons have been suppressed by electron cyclotron resonance heating. From the set of discharges studied in the present experiments, it has also been observed that the efficiency of runaway suppression by electron cyclotron resonance heating was apparently affected by two factors: electron cyclotron resonance heating power and duration. These results have been analysed by using a test particle model. The decrease of the toroidal electric field due to electron cyclotron resonance heating results in a rapid fall in the runaway electron energy that may lead to a suppression of runaway electrons. During electron cyclotron resonance heating with different powers and durations, the runaway electrons will experience different slowing down processes. These different decay processes are the major cause for influencing the efficiency of runaway suppression. This result is related to the safe operation of the Tokamak and may bring an effective control of runaway electrons.     

The anomalous penetration of intense circularly polarized electromagnetic beam through overdense magnetized plasma

The steady state nonlinear propagation of an intense, circularly polarized electromagnetic beam in an inhomogeneous magnetized plasma has been investigated in paraxial approximation. The laser induces a large oscillatory velocity on electrons, raising their mass and lowering the plasma frequency. Further, rising due to cyclotron resonance effect. The propagation of the electromagnetic waves in magnetized plasma in both the extraordinary and ordinary mode is analyzed. The nonlinearity in dielectric function is considered in presence of external magnetic field due to saturation effects for arbitrary large intensity, which leads to focusing/defocusing of the beam. The focusing effect along with magnetic field helps in the process of anomalous penetration of the beam by enhancing the depletion of the plasma from the axial region. The penetration increases with the incident beam power up to some critical value beyond which it rises abruptly when all electrons have been driven out of the axis. The cyclotron resonance effect awfully supports the laser beam to propagate inside the overdense plasma region. Numerical computations are performed for typical parameters of relativistic laser–plasma interaction applicable for underdense and overdense plasma.