Cyclotron resonance in a two-dimensional semimetal

Cyclotron resonance in a two-dimensional semimetal has been studied theoretically, keeping in mind recent experiments reported in Z. D. Kvon, S. N. Pamilov, S. D. Ganichev, et al., in Proceedings of the 14th International Conference on Narrow Gap Semiconductors and Systems (Sendai, Japan, 2009). Since the size of the sample is finite, the exciting microwave inhomogeneous and there is a plasma shift of resonance frequency. There are two magnetoplasmon branches in a two-component system, which undergo pseudocrossing under the found criterion. Resonance frequencies and intensities of absorption peaks have been found. The latter are complicated functions of the electron and hole densities.     

Nonlinear magnetotransport in a two-dimensional electron system in a square array of antidots in GaAs/AlAs heterostructures

Nonlinear magnetotransport of two-dimensional electrons in square antidot lattices prepared on the basis of selectively doped GaAs/AlAs heterostructures with the period that is much less than the electron mean free path in the initial GaAs quantum wells but is much larger than their Fermi wavelength has been studied. It has been shown that the character of the nonlinear transport of the two-dimensional electrons in the lateral lattices under study changes from classical to quantum with the decrease in the antidot radius. It has been found that the quantum lifetime increases in the magnetic field corresponding to the condition of equality of the cyclotron diameter of two-dimensional electrons and the antidot lattice period.     

Mesoscopic conductance fluctuations of a two-dimensional electron gas in a one-dimensional lattice of antidots

Mesoscopic conductance fluctuations of a two-dimensional electron gas in a one-dimensional periodic array of antidots have been studied experimentally, for the first time. The fluctuations show a quasiperiodic behaviour on magnetic field, with period corresponding to the quantization of magnetic flux through the area of a unit cell of the one-dimensional array. The existence of the quasiperiodic component is explained by an anomalous area distribution of interfering trajectories.     

Cyclotron resonance in a two-dimensional semimetal based on a HgTe quantum well

Microwave cyclotron resonance of electrons and holes at the metal-to-semimetal transition in HgTe quantum wells with an inversed band structure has been investigated. The resonance has been studied by measuring microwave photoresistance in the frequency range of 35–170 GHz. The effective cyclotron masses of electrons and holes have been determined. A shift of the cyclotron resonance of the two-dimensional electrons at the metal-to-semimetal transition possibly caused by plasma effects in the two-dimensional semimetal has been discovered.     

Cyclotron resonance of two-dimensional electrons forming wigner crystal

The cyclotron resonance peak shape is analysed for two-dimensional electrons interacting with surface vibrations of a medium. Explicit expressions for the broadening and shift of the peak are obtained at low and high electron densities.     

Cyclotron resonance studies on bulk and two-dimensional conduction electrons in InSe

Cyclotron resonance is reported for both bulk electrons and electrons bound to charged defect planes in the layer compound InSe. At temperatures below 20 K all carriers present are bound to defect planes and behave as two-dimensional accumulation layers. At higher temperatures the electrons are excited into bulk regions between the defects, and show three-dimensional, bulk behaviour. The conduction band is shown to exhibit an “anomalous anisotropy” with m_∥ = 0.08m₀ and m_⊥ = 0.14m₀. The bound, two-dimensional carriers exhibit a strong non-parabolicity, and show a band edge mass m_⊥ = 0.13 which is considerably lower than the bulk value possibly due to a reduction in the polaron constant in the degenerate electron gas.     

Cyclotron spin-wave in the 2D electron system

The cyclotron spin-wave mode of a two-dimensional electron system have been investigated by inelastic light scattering. It is observed at small electron filling factors, (v～0.1, when the electron system is spin-depolarized. As long as the electron system becomes fully spin-polarized (v>0.2), the cyclotron spin-wave disappears from the inelastic light scattering spectra. It reenters at electron filling factors v>1. Over the range of electron filling factors of 1<v<2, the cyclotron spin-wave energy is insensitive to both the experimentally accessible in-plane momenta and the electron concentration, whereas its inelastic light scattering efficiency is strongly influenced by the spin polarization of the electron system.     

Zero-bias tunneling anomaly in a two-dimensional electron system with disorder

The temperature dependence of a zero-bias anomaly in the tunneling conductance of an Al/δ-GaAs tunneling structure with a two-dimensional electron density in the δ-layer of 3.5 × 10¹² cm^?2 has been investigated. It has been shown that the respective drop Δρ(?, T) in the tunneling density of states ρ near the Fermi level E _F of the two-dimensional electron system depends logarithmically on the energy ? within the range of 2.7kT < |?| < ?/τ, where ? is measured with respect to E _F and τ is the momentum relaxation time of two-dimensional electrons. It has been found that the drop depth Δρ(0, T)/ρ is also proportional to ln(kT/?₀) in the temperature range T = 0.1–20 K and saturates below 0.1 K.     

Microwave photoresistance in a two-dimensional electron system with anisotropic mobility

The effect of microwave radiation on magnetotransport in single GaAs quantum wells with anisotropic mobility, whose maximum corresponds to the $[1\bar 10]$ direction and minimum to the [110] direction, is investigated using the Van der Pauw method. In samples shaped as squares with sides oriented along the $[1\bar 10]$ and [110] directions, giant oscillations of magnetoresistance arise under the effect of a microwave field for the both $[1\bar 10]$ and [110] orientations of the measuring current I _ac. In the anisotropic two-dimensional system under study, the relative amplitude of microwave photoresistance oscillations in a magnetic field weakly depends on the orientation of I _ac. At a temperature of 4.2 K and a microwave frequency of 130 GHz, magnetic field intervals characterized by close-to-zero resistance manifest themselves only for the case of the [110] orientation of I _ac. The aforementioned experimental results are qualitatively explained by a quasi-one-dimensional potential modulation of the two-dimensional electron gas in the [110] direction.     

Microwave photoresistance in a two-dimensional electron system with anisotropic mobility

The effect of microwave radiation on magnetotransport in single GaAs quantum wells with anisotropic mobility, whose maximum corresponds to the direction and minimum to the [110] direction, is investigated using the Van der Pauw method. In samples shaped as squares with sides oriented along the and [110] directions, giant oscillations of magnetoresistance arise under the effect of a microwave field for the both and [110] orientations of the measuring current I _ac. In the anisotropic two-dimensional system under study, the relative amplitude of microwave photoresistance oscillations in a magnetic field weakly depends on the orientation of I _ac. At a temperature of 4.2 K and a microwave frequency of 130 GHz, magnetic field intervals characterized by close-to-zero resistance manifest themselves only for the case of the [110] orientation of I _ac. The aforementioned experimental results are qualitatively explained by a quasi-one-dimensional potential modulation of the two-dimensional electron gas in the [110] direction. Original Russian Text ? A.A. Bykov, D.R. Islamov, A.V. Goran, A.K. Bakarov, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 12, pp. 891–895.     

Spin-Hall transport in a two-dimensional electron system with magnetic impurities

The spin Hall transport properties in a two-dimensional electron system with both Rashba spin-orbit coupling (SOC) and magnetic impurities are investigated. Electrons are scattered by impurities through an exchange interaction that leads to spin flip-flop processes and so changes the spin Hall effect induced by the SOC. The spin Hall conductance is calculated in a 4-terminal system using the Landauer-Buttiker formula and Green function approach. In comparison with the simulation results on nonmagnetic impurities doping systems, our results reveal that the spin Hall conductance is still nonzero in a system with a large density of magnetic impurities and a finite intensity of the exchange interaction between the electrons and impurities, and its sign may be altered when the doping density and interaction strength are large enough.     

Nonlinear magnetotransport in a two-dimensional electron system with anisotropic mobility

Nonlinear magnetotransport of two-dimensional electrons in modulation-doped GaAs/AlAs heterostructures with anisotropic mobility is investigated. The mobility attains its maximum and minimum values in the $\left[ {1\bar 10} \right]$ and [110] directions, respectively. It is found that, upon an increase in the direct electrical current I _dc though Hall bars oriented along the [110] direction, the transition of the two-dimensional system to the state with differential resistance r _xx ≈ 0 in a magnetic field occurs at a lower value of I _dc and is accompanied by a more pronounced “plunge” into the region of negative r _xx values as compared to bars oriented along the $\left[ {1\bar 10} \right]$ direction. The results are explained by the impact of mobility on the spectral diffusion of nonequilibrium charge carriers.