Photon-drag effect in a two-dimensional electron gas in high magnetic fields

We present the first measurements concerning the photon drag effect in a two-dimensional electron gas based on intersubband transitions in high magnetic fields. It is shown that the excitation mechanism of the drag voltage in a magnetic field differs obviously from the case of zero magnetic field. The longitudinal as well as the Hall drag voltage show strong oscillations around zero when the magnetic field is swept. Both consist of a B-symmetrical and an antisymmetrical part with the same periodicity in B as the magnetoresistanceR_xx. The drag voltage oscillations are strongly correlated to the relative position of Fermi energy and Landau levels and are independent of the photon energy in the range of usable laser lines.     

Occurrence of intersubband polaronic repellons in a two-dimensional electron gas

Counteracting electron-phonon and electron-electron interaction in the optical absorption spectra of a quantum well intersubband system can have a significant impact on the line shape and line width of optical transitions at low temperatures. In particular, polaronic repellons can be formed due to an attractive intersubband polaron-polaron interaction. At low temperatures and for properly chosen densities; this effect can lead to a line broadening of the intersubband transition, even in a weak coupling regime.     

Shake-up processes in intersubband magneto-photoabsorption of a two-dimensional electron gas

I theoretically study shake-up processes in photoabsorption of an interacting low-density two-dimensional electron gas (2DEG) in magnetic fields. Such processes, in which an incident photon creates an electron–hole pair and simultaneously excites one electron to one of the higher Landau levels, were observed experimentally [Phys. Rev. Lett. 79 (1997) 3974] and were called combined exciton-cyclotron resonance (ExCR). The recently developed theory of ExCR [Phys. Rev. B 64 (2001) 241101] allows for a consistent treatment of the Coulomb correlations, establishes the exact ExCR selection rules, and predicts the high-field features of ExCR. In this work, I generalize the existing theory of high-field ExCR in the 2DEG to the case when the hole is excited to higher hole Landau levels.     

Phase-resolved nonlinear response of a two-dimensional electron gas under femtosecond intersubband excitation

Strong electric-field transients resonant to intersubband transitions in n-type modulation-doped GaAs/AlGaAs quantum wells induce coherent Rabi oscillations, which are demonstrated by a phase-resolved measurement of the light emitted by the sample. The time evolution of the intersubband polarization is influenced by Coulomb-mediated many-body effects. The subpicosecond period and the phase of the Rabi oscillations are controlled by the properties of the midinfrared driving pulse.     

Quantum pump effect induced by a linearly polarized microwave in a two-dimensional electron gas

A quantum pump effect is predicted in an ideal homogeneous two-dimensional electron gas (2DEG) that is normally irradiated by linearly polarized microwaves (MW). Without considering effects from spin-orbital coupling or the magnetic field, it is found that a polarized MW can continuously pump electrons from the longitudinal to the transverse direction, or from the transverse to the longitudinal direction, in the central irradiated region. The large pump current is obtained for both the low frequency limit and the high frequency case. Its magnitude depends on sample properties such as the size of the radiated region, the power and frequency of the MW, etc. Through the calculated results, the pump current should be attributed to the dominant photon-assisted tunneling processes as well as the asymmetry of the electron density of states with respect to the Fermi energy.     

The microwave Hall effect of a two-dimensional electron gas

The integer Quantum Hall effect has been recently observed in the Hall conductivity _xy at microwave frequencies. Here we present a calculation of the wave propagation in the crossed waveguide system used in the experiments. The field pattern is more complicated than in the case of a pure plane wave. The essential result, however, remains unchanged: The field strength in the second (crossed) waveguide is proportional to _xy of the two-dimensional electron gas. Dedicated to Professor Karlheinz Seeger on the occasion of his 60th birthday     

Compton effect in and power absorption by an electron gas

An analysis is made of Compton scattering by an electron gas. The power absorption and heating of an electron gas are calculated. The possible measurement of the intensity of intense coherent light beams is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 95–99, September, 1970.     

Optical detection of the absorption of acoustical phonons by a two-dimensional electron gas in a magnetic field

The effect of absorption of nonequilibrium acoustical phonons on the intensity of recombination of a two-dimensional electron gas in a magnetic field is investigated. The nonequilibrium acoustical phonons are emitted in the relaxation of electrons in a tunnel junction deposited on the back side of a sample with a two-dimensional electronic channel. It is demonstrated that the optical signal showing the intensity of the recombination of nonequilibrium electrons from a photoexcited size-quantization subband can serve as a sensitive detector of acoustical phonons. Because the general heating of two-dimensional carriers and the intersubband transitions stimulated by the absorption of nonequilibrium acoustical phonons lead to effects of different sign, the useful signal can be discriminated unambiguously. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 1, 30–35 (10 January 1999)     

Solitons in a two-dimensional electron gas

The non-linear spectrum of a two-dimensional electron gas (2-DEG) formed at the interface of a heterostructure is investigated. This spectrum is found to contain a new type of localized excitation exhibiting soliton behavior. A matrix formulation of the model equations permits the extraction of the equation of evolution in space for these excitations. Results are presented for the boundary value problem excited by temporal Gaussian pulses.     

Observation of intersubband excitations in a multilayer two dimensional electron gas

We report the observation, by resonant inelastic light scattering, of intersubband excitations of the multilayer two dimensional electron gas, in modulation doped GaAsAlGaAs heterojunction superlattices. These are the first measurements of these transitions by any technique, and furnish intersubband energies in good agreement with calculated values. The spectral bands are broad, and nearly Lorentzian in shape: the implied relaxation rates scale linearly with band energy and are significantly faster than transport relaxation rates. Finally, the polarized spectra reveal differences between spin-flip and non spin-flip excitations which are unique to multilayer two dimensional electron gases.     

Electric-tunable magnetoresistance effect in a two-dimensional electron gas modulated by hybrid magnetic-electric barrier nanostructure

The electric-tunable spin-independent magnetoresistance effect has been theoretically investigated in ballistic regime within a two-dimensional electron gas modulated by magnetic-electric barrier nanostructure. By including the omitted stray field in previous investigations on analogous structures, it is demonstrated based on this improved approximation that the magnetoresistance ratio for the considered structure can be efficiently enhanced by a proper electric barrier up to the maximum value depending on the specific magnetic suppression. Besides, it is also shown the introduction of positive electrostatic modulation can effectively overcome the degradation of magnetoresistance ratio for asymmetric configuration and enhance the visibility of periodic pattern induced by the size effect, while for an opposite modulation the system magnetoresistance ratio concerned may change its sign.     

Magnetotransport in a modulated two-dimensional electron gas

We propose a semiclassical theory of dc magnetotransport in a two-dimensional electron gas modulated along one direction with weak electrostatic modulations. We show that oscillations of the magnetoresistivity ρ_∥ corresponding to the current driven along the modulation lines observed at moderately low magnetic fields can be explained as commensurability oscillations.     

Spin Hall effect generated by a temperature gradient and heat current in a two-dimensional electron gas

We predict an intrinsic thermo-spin Hall effect, namely, that a transverse spin current is generated by the temperature gradient and the heat current in a disorder-free two-dimensional electron gas (2DEG) with finite spin–orbit coupling. There exist two classes of contributions to the thermal spin Hall effect, corresponding to a 2DEG contacting two reservoirs at different temperatures and to a 2DEG separated from the reservoirs by insulating spacers, respectively. It is shown that the thermal spin Hall current can be generated not only by the temperature gradient directly but also by the thermoelectric effect.