A. A. Sherstobitov

Quantum corrections to the conductivity of a natural Nd2−x CexCuO4 superlattice

Temperature and magnetic field dependences of the resistivity and Hall coefficient in layered single-crystal Nd2−xCexCuO4 (x = 0.12) films are experimentally investigated and analyzed. It is shown that this material clearly exhibits quantum effects characteristic of 2D semiconductor structures: negative magnetoresistance caused by suppression of the interference quantum correction by a magnetic field, a near-logarithmic temperature dependence of the conductivity, and a temperature dependence of the Hall coefficient related to e-e interaction. It is shown that, when analyzing experimental data, it is necessary to take interlayer transitions into account. Such an approach provides quantitative agreement between experiment and the standard theory of quantum corrections.

Two-dimensional semimetal in wide HgTe quantum wells: Charge-carrier energy spectrum and magnetotransport

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.

Low-field anomaly of the hall effect in disordered two-dimensional systems

This study is devoted to investigation of the nonlinear behavior of the Hall resistance in low magnetic fields. When investigating two-dimensional electron gas in single GaAs/InxGa1 − xAs/GaAs quantum wells, it is shown that the anomaly of the Hall effect in disordered systems can be described taking into account the second-order quantum corrections to conductivity.

Nonohmic conductivity as a probe of crossover from diffusion to hopping in two dimensions

We show that the study of conductivity nonlinearity gives a possibility to determine the condition when the diffusion conductivity changes to the hopping one with increasing disorder. It is experimentally shown that the conductivity of single quantum well GaAs/InGaAs/GaAs heterostructures behaves like diffusive one down to value of order

Zeeman splitting of the conduction band of HgTe quantum wells with a semimetallic spectrum

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Percolation and the electron–electron interaction in an array of antidots

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Energy spectrum and transport in narrow HgTe quantum wells

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.

Electron transport effects in the IR photoconductivity of InGaAs/GaAs structures with quantum dots

A square lattice of microcontacts with a period of 1 μm in a dense low-mobility two-dimensional electron gas is studied experimentally and numerically. At the variation of the gate voltage Vg, the conductivity of the array varies by five orders of magnitude in the temperature range T from 1.4 to 77 K in good agreement with the formula σ(Vg) = (Vg−Vg*(T))β with β = 4. The saturation of σ(T) at low temperatures is absent because of the electron–electron interaction. A random-lattice model with a phenomenological potential in microcontacts reproduces the dependence σ(T, Vg) and makes it possible to determine the fraction of microcontacts x(Vg, T) with conductances higher than σ. It is found that the dependence x(Vg) is nonlinear and the critical exponent in the formula σ ∝ − (x - 1/2)t in the range 1.3 < t(T, Vg) < β.

Zeeman Splitting of Electron Spectrum in HgTe Quantum Wells Near the Dirac Point

The results of an experimental study of the transport phenomena and the hole energy spectrum of two-dimensional systems in the quantum well of HgTe zero-gap semiconductor with normal arrangement of quantum-confinement subbands are presented. An analysis of the experimental data allows us to reconstruct the carrier energy spectrum near the hole subband extrema. The results are interpreted using the standard kP model.

Zeeman splitting of conduction band in HgTe quantum wells near the Dirac point

We have studied the temperature dependence of the Hall effects in multilayer selectively doped InGaAs/GaAs heterostructures with quantum dots (QDs). It was found that structures possessing photoconductivity in the IR range exhibit a sharp (nearly exponential) growth of the conductivity and Hall mobility in the temperature interval from 8 to 30 K at a virtually constant Hall coefficient and electron density. A new mechanism of the lateral photoconductivity in the structures with QDs is proposed which is related to the change in the electron mobility in the two-dimensional channel as a result of a decrease in the Coulomb scattering on charged QDs.