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An Erratum to this paper has been published: https://doi.org/10.1134/S0021364022340045

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.

Large-scale anisotropy or so-called sidereal-diurnal wave has been detected in the PAMELA satellite experiment in the time interval of 2006–2014. The magnitude of anisotropy has been measured simultaneously for the Southern and Northern Hemispheres in the equatorial coordinate system. The results confirm the data of ground-based experiments.

For the Hg1−x Cd x Te-based structures, it is shown that the transition from the direct to invertеd spectrum is accompanied by the sign change for the signals related to the terahertz photoconductivity and to the magnetophotogalvanic effect. Within the range of chemical compositions corresponding to the inverted spectrum, the photoconductivity kinetics exhibits specific features, which can result from the surface topological states.

Information on the density of states of two-dimensional Dirac fermions in a 6.6-nm-thick HgTe quantum well that corresponds to a transition from the direct to inverted spectrum is obtained for the first time by means of capacitance measurements. It is found that the density of states of Dirac electrons is a linear function of the Fermi energy at EF > 30 meV with the corresponding velocity vDF = 8.2 × 105 m/s. At lower energies, this dependence deviates from the linear law, indicating a strong effect of disorder, which is associated with fluctuations of a built-in charge, on the density of states of the studied system near the Dirac point. At negative energies, a sharp increase in the density of states is observed, which is associated with the tail of the density of states of valleys of heavy holes. The described behavior is in agreement with the proposed model, which includes both the features of the real spectrum of Dirac fermions and the effect of the fluctuation potential.

The terahertz resistive response of a two-dimensional topological insulator in a HgTe quantum well in the quasiballistic transport regime is studied. The photoresistance appearing only near the charge neutrality point is detected. The application of the magnetic field up to 4 T in the plane of the quantum well results in an increase in the photoresistance in the peak and in the expansion of the region near the charge neutrality point where it exists. The reported results imply that the observed photoresistance is due to transitions involving edge dispersion branches of the two-dimensional topological insulator.

The quantum Hall effect (QHE) in a HgTe/CdHgTe double quantum well (DQW) with a tunneling-transparent barrier and the energy spectrum resembling the band structure of bilayer graphene has been investigated. An experimental manifestation of a tunnel gap between the states of light carriers seen as a magnetoresistance (MR) peak in the in-plane magnetic field has been discovered. An unusual structure of the QHE has been observed in a sample with hole conductivity: there is a pronounced peak on a plateau with the number i = 2 and the slopes of this anomalous peak correspond to two peaks of the longitudinal MR. On the other hand, a stable 2–1 plateau–plateau transition has been observed in much higher fields with the position of this transition corresponding to a considerably higher hole density than follows from the pattern of the QHE in weak fields. The anomalous peak is interpreted as a reentrant QHE between the 2–1–2 states. The position of the anomalous peak is immune to IR illumination and the tilting angle of the magnetic field, although these factors strongly affect its amplitude. According to comparison with the calculated structure of magnetic levels, the anomalous peak is attributed to crossing of electron-like and hole-like levels in the valence band. The difference between the hole densities found in weak field and from the 2–1 transition in strong fields is attributed to the effects of redistribution of holes between the localized states in sideband maxima of the valence subband and the ones delocalized in the overlapping levels of light holes.

The mobility of Dirac electrons (DEs) in HgTe quantum wells with the thickness close to the critical value corresponding to the transition from the direct to inverted spectrum has been studied experimentally and theoretically. The nonmonotonic dependence of this mobility on the electron density is found experimentally. The theory of DE scattering on impurities and fluctuations of the thickness of a well caused by its roughnesses is elaborated. This theory is in good agreement with experiment and explains the observed nonmonotonicity by the decrease in the ratio of the de Broglie wavelength of DEs to the characteristic size of the roughness with the increase in their concentration.

Shubnikov–de Haas oscillations in Hg1-xCdx Te/HgTe/Hg1-xCdxTe structures with the widths of a well of 16 and 20 nm have been investigated in tilted magnetic fields. The spin-to-orbital splitting ratio in the conduction band has been found in a wide range of electron densities. The magnitude and density dependence of the ratio agree fairly well with the calculations of the spectrum in the 8-band kP model. It has been shown that the effective g factor is anisotropic, g|| < g┴. The anisotropy is very high at low densities but decreases rapidly with an increase in the density, approaching unity at ne = (3−4) × 1011 cm-2.