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Shubnikov–de Haas oscillations and magneto-intersubband oscillations of the magnetoresistance in structures with single HgTe quantum wells with a width of 10−18 nm have been experimentally investigated. The conduction band spectrum in these arrays is split by the spin–orbit interaction. This leads to beats in the Shubnikov−de Haas oscillations and gives rise to low-frequency magneto-intersubband oscillations. The mutual positions of the antinodes of the Shubnikov−de Haas oscillations and the peaks in the magneto-intersubband oscillations are unusual: at low magnetic fields, they are opposite to theoretical predictions. The measurements in high magnetic fields, at which the relative amplitude of Shubnikov–de Haas oscillations exceeds 0.2–0.3, show a change in the mutual positions of the antinodes of the Shubnikov–de Haas oscillations and the peaks in low-frequency oscillations. Numerical calculations and additional measurements at different temperatures suggest that the observed effects are due to magnetic-field-induced oscillations of the Fermi level. [ABSTRACT FROM AUTHOR]

The magnetic field and temperature dependences of longitudinal magnetoresistance and the Hall effect have been measured in order to determine the energy spectrum of the valence band in HgTe quantum wells with the width dQW = 20–200 nm. The comparison of hole densities determined from the period of Shubnikov–de Haas oscillations and the Hall effect shows that states at the top of the valence band are doubly degenerate in the entire dQW range, and the cyclotron mass determined from the temperature dependence of the amplitude of Shubnikov–de Haas oscillation increases monotonically from to ( is the mass of the free electron) with increasing hole density from to cm–2. The determined dependence has been compared to theoretical dependences calculated within the four-band kP model. These calculations predict an approximate stepwise increase in owing to the pairwise merging of side extrema with increasing hole density, which should be observed at and 4 × 1010 cm–2 for dQW = 20 and 200 nm, respectively. The experimental dependences are strongly inconsistent with this prediction. It has been shown that the inclusion of additional factors (electric field in the quantum well, strain) does not remove the contradiction between the experiment and theory. Consequently, it is doubtful that the mentioned kP calculations adequately describe the valence band at all dQW values. [ABSTRACT FROM AUTHOR]

Magneto-intersubband oscillations (MISOs) in single quantum wells of the gapless semiconductor HgTe have been studied experimentally. It has been shown that, in contrast to MISOs in double quantum wells based on broadband semiconductors GaAs and InGaAs and theoretical predictions, magnetic fields at which antinodes of high-frequency oscillations are observed coincide with minima rather than with maxima of MISOs of the magnetoresistance ρxx. It has been assumed that this feature is due to the suppression of the resonance of the probability of transitions between Landau levels of two spectral branches split by the strong spin—orbit coupling. [ABSTRACT FROM AUTHOR]

The Zeeman splitting of the conduction band in the HgTe quantum wells both with normal and inverted spectrum has been studied experimentally in a wide electron density range. The simultaneous analysis of the Shubnikov-de Haas oscillations in low magnetic fields at different tilt angles and of the shape of the oscillations in moderate magnetic fields gives a possibility to find the ratio of the Zeeman splitting to the orbital one and anisotropy of g-factor. It is shown that the ratios of the Zeeman splitting to the orbital one are close to each other for both types of structures, with a normal and inverted spectrum and they are close enough to the values calculated within kP method. In contrast, the values of g-factor anisotropy in the structures with normal and inverted spectra are strongly different and for both cases differ significantly from the calculated ones. We assume that such disagreement with calculations is a result of the interface inversion asymmetry in the HgTe quantum well, which is not taken into account in the kP calculations. [ABSTRACT FROM AUTHOR]

The magnetoresistivity and the Hall and Shubnikov-de Haas effects in heterostructures with a single 20.2-nm-wide quantum well made from the gapless semiconductor HgTe are studied experimentally. The measurements are performed on gated samples over a wide range of electron and hole densities. The data obtained are used to reconstruct the energy spectrum of electrons and holes in the vicinity of the extrema of the quantum-confinement subbands. It is shown that the charge-carrier dispersion relation in the investigated systems differs from that calculated within the framework of the conventional kp model. [ABSTRACT FROM AUTHOR]

Dependences of electrical conductivitys on temperature and electric-field strength were studied in a wide range of conductivities (from σ ≪e[SUP2]/ħ to σ ≫ e[SUP2]/ ħ) in GaAs/InGaAs/GaAs structures with a two-dimensional electron gas. It is shown that one cannot reliably determine the mechanism of conductivity from the temperature dependence of ohmic conductivity. Studies of nonohmic conductivity make it possible to determine the range of values of low-temperature conductivity that correspond to the transition from the diffusion mechanism of conductivity to the hopping mechanism. It is shown that, in the structures under investigation, the conductivity is still controlled by diffusion as the degree of disorder increases even when the low-temperature conductivity is much lower than e[SUP2]/ ħ. [ABSTRACT FROM AUTHOR]