Cyclotron resonance and screening effects in GaAs-GaAlAs heterojunctions

Cyclotron resonance absorption has been studied in several high quality GaAs-GaAlAs heterojunctions. The dependence of the effective mass upon frequency, electron concentration and temperature has been measured and gives a nonparabolicity that is some 20% smaller than that measured in bulk GaAs. This is contrary to simple theory which predicts an enhanced polaron contribution in two-dimensional systems, and we attribute this difference to strong screening of the electron-phonon interaction. The presence of a small magnetic field component parallel to the interface introduces a coupling at energies corresponding to the electric subband separations. These couplings have been studied as a function of electron concentration and the results interpreted in terms of changes in the depletion charge in the GaAs layer.     

Filling-factor-dependent magnetophonon resonance in graphene

We describe a peculiar fine structure acquired by the in-plane optical phonon at the Gamma point in graphene when it is brought into resonance with one of the inter-Landau-level transitions in this material. The effect is most pronounced when this lattice mode (associated with the G band in graphene Raman spectrum) is in resonance with inter-Landau-level transitions 0 --> +, 1 and -, 1 --> 0, at a magnetic field B{0} approximately 30 T. It can be used to measure the strength of the electron-phonon coupling directly, and its filling-factor dependence can be used experimentally to detect circularly polarized lattice vibrations.     

Hot-carrier magnetophonon resonance in CdxHg1−xTe

Resistance oscillations and voltage-current characteristics have been examined for Cd_xHg_1–xTe crystals on both sides of the transition from the gap-free phase to the narrow-gap phase in strong electric fields (1相似文献   

Observation of magnetophonon resonance of Dirac fermions in graphite

Coherent coupling of Dirac fermion magnetoexcitons with an optical phonon is observed in graphite as marked magnetic-field dependent splittings and anticrossing behavior of the two coupled modes. The sharp magnetophonon resonance occurs in regions of the graphite sample with properties of superior single-layer graphene having enhanced lifetimes of Dirac fermions. The greatly reduced carrier broadening to values below the graphene electron-phonon coupling constant explains the appearance of sharp resonances that reveal a fundamental interaction of Dirac fermions.     

Structure of magnetophonon resonance under hot electron conditons in n-InSb

It is shown that a series of hot electron induced magnetophonon resonances recently reported can be interpreted as a hot electron induced shift of the fundamental resonance.     

Theory of hot electron magnetophonon resonance in longitudinal magnetic fields

Longitudinal magnetoresistance of hot electrons in n—InSb at low temperatures is calculated taking into account the quantization of the conduction band into Landau subbands. Negative magnetoresistance and magnetophonon resonance minima are obtained as combined effects of inter-subband transition and optical phonon emission.     

Thermoelectric power of GaAs-GaAlAs heterostructures in high magnetic fields

We report measurements of the diagonal component of the thermoelectric power in a superlattice and a heterojunction of GaAs and GaAlAs. The qualitative variation of the thermopower with magnetic field is in agreement with both theoretical studies and previous experimental measurements. Quantitatively, the behaviour of the superlattice agrees with calculations for an ideal two-dimensional system, but both the magnitude and temperature dependence of the thermopower in the heterojunctions cannot be explained by existing theories.     

Photo-induced magnetophonon resonance in n-InSb at 4.2°K

Spin-flip and two-phonon as well as normal magnetophonon resonance are observed in CO₂-laser-irradiated photoconductivity in n-InSb at 4.2°K. The effects are attributed to the resonant cooling of photo-excited electrons due to optical phonon emission.     

A study of intervalley scattering in n-Si by stress-dependent longitudinal magnetophonon resonance

The stress dependence of the amplitude and position of the magnetophonon extrema of n-Si are employed to distinguish the f- and g-type intervalley scattering series. The sign of the extrema of the g-T.A. series changes at a critical stress. The measurements locate the conduction band minima at (0.85 ± 0.01, 0, 0) in the reduced Brillouin zone.     

Collapse of resonance in quasi-one-dimensional quantum channels

We study the resonance structure of the conductance (transmissivity) of a quasi-one-dimensional channel that contains an attractive impurity of finite dimensions and derive an exact expression for the scattering matrix. We show that an impurity of finite dimensions may cause a set of Fano resonances to appear in the transmissivity. We also find that due to the coherent interaction the Fano resonances can collapse and discrete levels may appear in the continuum. Finally, we establish the wave function of the discrete levels and study the channel transmissivity in the critical regime. Zh. éksp. Teor. Fiz. 116, 263–275 (July 1999)     

The magnetophonon effect in n-PbTe

We have observed magnetophonon resonances in degenerate n-PbTe. They arise from intravelley scattering of electrons with the absorption of unscreened long wavelength LO-phonons. The electron effective mass parameters obtained from this experiment are: m_t = 0.029 m₀ and K = 8.7 for a sample having n = 5.0 × 10¹⁷/cm³ at T = 77°.     

Study and characterization by magnetophonon resonance of the energy structuring in GaAs/AlAs quantum-wire superlattices

We present the characterization of the band structure of GaAs/AlAs quantum-wire 1D superlattices performed by magnetophonon resonance with pulsed magnetic fields up to 35 T. The samples, generated by the ‘atomic saw method’ from original quantum-well 2D superlattices, underwent substantial modifications of their energy bands built up on the X-states of the bulk. We have calculated the band structure by a finite element method and we have studied the various miniband structures built up of the massesm_tandm_lof GaAs and AlAs at the point X. From an experimental point of view, the main result is that in the 2D case we observe only resonances when the magnetic fieldBis applied along the growth axis whereas in the 1D case we obtain resonances in all magnetic field configurations. The analysis of the maxima (or minima forB//E) in the resistivity ρ_xyas a function ofBallows us to account, qualitatively and semi-quantitatively, for the band structure theoretically expected.     

Electrical properties of bilayer heterojunctions in a strong magnetic field

The electrical properties of bilayer heterojunctions in a strong magnetic field at low temperatures have been considered. It has been shown that both the ohmic and Hall conductivities decrease exponentially due to the formation of neutral pairs if the electric fields in the two layers are parallel. In the antiparallel fields, the Hall conductivity is still determined by the activation energy of the excited electrons and decreases exponentially, but the ohmic conductivity decreases much slower, proportional to the temperature square.