After a brief survey of theoretical concepts for the two-parameter scaling theory in the integer quantum Hall effect regime, a comprehensive set of early, recent and new experimental results on constructing scaling diagrams for conductance in 2D semiconductor structures, as well as in graphene is displayed. A comparative analysis of scaling diagrams obtained from experimental data with calculated ones is carried out.

In the n-InGaAs/GaAs double quantum well, the suppression of resonant resistance by an in-plane magnetic field B <= 9 T in the temperature range T = (1.8-70) K is studied. The electron quantum lifetime, aq, is determined and the contributions of various scattering mechanisms to aq(T) are separated. It is shown that the observed nonmonotonic temperature dependence of the electron quantum lifetime is due to a combination of the interference contribution from the exchange electron-electron interaction in the ballistic regime and the inelastic electronelectron scattering in the diffusion regime (Fukuyama-Abrahams mechanism).

A brief review of the galvanomagnetic properties of highly anisotropic cuprate superconductors is presented, with an emphasis on the internal Josephson effect, which naturally exists in multilayer HTSC crystals. The transport of charge carriers perpendicular to the layers in such materials occurs by successive tunneling of quasiparticles (or Cooper pairs) between highly conducting (or superconducting) CuO2, layers through intermediate buffer layers. Currently available results on the nonmetallic conductivity along the c-axis in the normal state are analyzed, as are data on the distinctive branched current-voltage characteristics in the superconducting state, which are clear experimental manifestations of tunneling effects in layered cuprate superconductors.

The paper presents experimental results of the appearance of a voltage at the potential contacts in the absence of an external current through a sample in the plateau region of the quantum Hall effect in a heterostructure with an InGaAs/InAlAs quantum well. The occurrence of a voltage is associated with the nonequivalence of the edge current in the potential contact areas in a magnetic field in a system with a two-dimensional electron gas.

The current-voltage (I-V) properties along the c axis on Nd2-xCexCuO4/SrTiO3 epitaxial films with x = 0.145, 0.15 were investigated. For all the samples it has been established that the I-V characteristics exhibit several resistive branches, which correspond to the resistive states of individual Josephson junctions. The results confirm the idea of a tunneling mechanism between the CuO2 layers (superconductor - insulator - superconductor junction) for the investigated Nd2-xCexCuO4 compound. The I-V dependence of this compound with x = 0.15 points out on the nonmonotonic nature of the d-wave or anisotropic s-wave symmetry order parameter associated with the coexistence of superconductivity and antiferromagnetic fluctuations.

A WTe2 single crystal was grown by the chemical vapor transport method, and its electrical resistivity and galvanomagnetic properties were investigated. Single-band and two-band models were used to estimate the concentration and mobility of charge carriers in WTe2 at temperatures from 4.2 to 150 K.

A magnetic field parallel to the layers of a double quantum well with conventional semiconductor constituents leads to a relative shift of the conduction band spectra of the constituent layers along the wave vector perpendicular to the field. If the states of the layers are tunnel-coupled, a tunneling gap is formed at the intersection of the single-layer spectra and is shifted upward with increasing field. This leads to striking features in the magnetoresistance caused by intersections of the Fermi level with the edges of the tunneling gap. Similar studies of transformations of the spectrum of the double quantum well in a HgTe/CdHgTe heterosystem, which has a p-type conductivity and HgTe layers with a gapless inverse energy spectrum, are reported in this work. Our experiments and corresponding calculations in the eight-band kp approach indicate that the evolution of the magnetoresistance with the variation of the in-plane field here has a much more complex and diverse character depending qualitatively on the thickness of the layers.

A magnetic field parallel to the layers of a double quantum well with conventional semiconductor constituentsleads to a relative shift of the conduction band spectra of the constituent layers along the wave vector perpendicularto the field. If the states of the layers are tunnel-coupled, a tunneling gap is formed at the intersectionof the single-layer spectra and is shifted upward with increasing field. This leads to striking features in themagnetoresistance caused by intersections of the Fermi level with the edges of the tunneling gap. Similarstudies of transformations of the spectrum of the double quantum well in a HgTe/CdHgTe heterosystem,which has a p-type conductivity and HgTe layers with a gapless inverse energy spectrum, are reported in thiswork. Our experiments and corresponding calculations in the eight-band kp approach indicate that the evolutionof the magnetoresistance with the variation of the in-plane field here has a much more complex anddiverse character depending qualitatively on the thickness of the layers.

fominykh@imp.uran.ru Abstract. A WTe2 single crystal was grown by the chemical vapor transport method, and its electrical resistivity and galvanomagnetic properties were investigated. Single-band and two -band models were used to estimate the concentration and mobility of charge carriers in WTe2 at temperatures from 4.2 to 150 K.

In quantum wells (QWs) formed in HgCdTe/CdHgTe heterosystems with a variable composition of Cd(Hg), Shubnikov-de-Haas (SdH) oscillations are investigated to characterize the Rashba-type spin-orbit coupling in QWs with both a normal and inverted band structure. Several methods of extracting the Rashba spin-splitting at zero magnetic field and their magnetic field dependences from the beatings of SdH oscillations are used for greater reliability. The large and similar Rashba splitting (25–27 meV) is found for different kinds of spectrum, explained by a significant fraction of the p-type wave functions, in both the E1 subband of the sample with a normal spectrum and the H1 subband for the sample with an inverted one.

A stepwise behavior of the Hall magnetoresistance ρ_yx(B) with an almost vertical increase around zero and a further trend close to h/e^2 has been revealed in a double quantum well consisting of two 8.5-nm-thick HgTe layers separated by a 3-nm barrier. The band structure of the double quantum well is characterized by a sharp maximum in the center of the Brillouin zone, which is close in energy to the lateral maximum. The observed sharp increase in ρ_yx(B) near zero is consistent with a vanishingly low concentration of light holes at this maximum, but the further almost horizontal behavior is inconsistent with the classical description of ρ_yx(B) for a high concentration of low-mobility holes at the lateral maximum and implies quantum effects. A high sensitivity of the observed behavior of ρ_yx(B) to external fields (electric field perpendicular to the layers and a parallel magnetic field) has been detected in agreement with change in fine balance of the positions of the central and lateral maxima. It has been shown that this property occurs because the double quantum well has a specific dipole moment distinguishing it from the single quantum well with similar features of the band structure; consequently, the response of the single quantum well should be much weaker.

The effects observed in the Shubnikov–de Haas oscillation regime in the HgCdTe/HgTe/HgCdTe heterostructure with a wide (20.3 nm) HgTe quantum well with an inverted band structure are discussed. In a topologically trivial 2D system, a π-shift of magnetooscillation phase is found. A thorough experimental study and theoretical analysis of the data is presented to understand the physical causes of this anomalous phase shift. The effective electron mass m c / m 0 = (0.022 ± 0.002) obtained from the region of doubly degenerate magnetoresistance peaks is approximately half the theoretical estimates. In the region of stronger magnetic fields, for non-degenerate magnetoresistance peaks, we have m c / m 0 = (0.034 ± 0.003), which is in good agreement with both theoretical predictions and experimental results obtained from the analysis of activation conductivity in the quantum Hall effect regime. The reasons for this discrepancy are discussed.

Quasiclassical calculations of the effective cyclotron mass and the spectrum of Landau levels have been carried out for carriers of the size-quantized H2 subband with a nonmonotonic dispersion law, which forms a valence band of 20.5-nm-wide HgTe quantum well with an inverted band structure. The model of the so-called “extremum loop”, previously developed by Rashba and Sheka for semiconductors with a wurtzite lattice, has been used for calculations. The results obtained are compared both with the empirical picture and with quantum-mechanical calculations of the Landau level spectrum for the HgTe quantum well in the semimetallic phase.

Ytterbium and holmium titanates have been synthesized and their dielectric and magnetic properties have been investigated. The frequency dependences of the permittivity at T = 77 and 300 K, and measured magnetization curves and temperature dependences of the magnetic susceptibility in fields up to 30 kOe and at temperatures from 2 K to 50 K have been obtained. The properties of the doped and undoped titanates have been compared. Based on the temperature dependences of the magnetic susceptibility, the magnetic dipole and exchange couplings in the titanates have been analyzed.

The effects observed in the Shubnikov - de Haas oscillation regime in the HgCdTe/HgTe/HgCdTe heterostructure with a wide (20.3 nm) HgTe quantum well with an inverted band structure are discussed. In a topologically trivial 2D system, Pi(Greek letter) - shift of magnetooscillation phase is found. A thorough experimental study and theoretical analysis of the data is presented to understand the physical causes of this anomalous phase shift. The value of the effective electron mass m_c/m_0 = (0.022+-0.002), obtained from the region of doubly degenerate peaks of magnetoresistance, is approximately half the theoretical estimates. In the region of stronger magnetic fields for nondegenerate peaks of magnetoresistance, we have m_c/m_0 = (0.034+-0.003), which is in good agreement with both theoretical predictions and experimental results obtained from the analysis of activation conductivity in the quantum Hall effect regime. The reasons for this discrepancy are discussed.

The results of the longitudinal and Hall magnetoresistivity measurements in the Shubnikov - de Haas oscillation regime for the HgCdTe/HgTe/HgCdTe heterostructures with a wide (20.3 nm) HgTe quantum well are presented. An anomalous phase shift of magneto-oscillations is detected in the region of spin-unsplit peaks in contradiction with a conventional situation in 2D systems. It is shown that the observed features are associated with the inverted nature of the spectrum in the size-quantized H1 subband of the investigated HgTe quantum well. The results obtained are compared with the phase shift effects of both the magneto-oscillations and plateaus of the quantum Hall effect in monolayer graphene and in semimagnetic HgMnTe quantum wells.

The longitudinal ρxx(B, T) and Hall ρxy(B, T) resistances are experimentally investigated in n-InGaAs/GaAs nanostructures with a single and double quantum wells in the magnetic field range B = 0–2.5 T and temperatures T = 1.8–20 K. It is shown that the origin of the temperature-independent point located at ωcτ≅1 on the ρxx(B, T) curves is due to the combined action of the classical cyclotron motion and the quantum interference effects of weak localization and electron-electron interaction. The results obtained indicate that the transition from the dielectric phase to the phase of the quantum Hall effect is a crossover from weak localization (quantum interference effects in a weak magnetic field) to strong localization in quantizing magnetic fields in the quantum Hall effect regime.

The results of the longitudinal and Hall magnetoresistivity measurements in the Shubnikov - de Haas oscillation regime for the HgCdTe/HgTe/HgCdTe heterostructures with a wide (20.3 nm) HgTe quantum well are presented. An anomalous phase shift of magneto-oscillations is detected: in the region of spin-unsplit peaks the longitudinal resistivity maxima are located at even filling factor numbers in contradiction with a conventional situation in 2D systems. It is shown that the observed features are associated with the inverted nature of the spectrum in the investigated quantum well with the electron-type conduction along the size-quantized subband H1 of HgTe band {\Gamma}8, for which the spin splitting is comparable to (and even greater than) the orbital one. The results obtained are compared with the phase shift effects of both magneto-oscillations and the plateau of the quantum Hall effect in monolayer graphene.

We report on the observation of an unconventional structure of the quantum Hall effect (QHE) in a p-type HgTe/CdxHg1-xTe double quantum well (DQW) consisting of two HgTe layers of critical thickness. The observed QHE is a reentrant function of magnetic field between two i = 2 states (plateaus at rho(yx) = h/ie(2)) separated by an intermediate i = 1 state in the shape of a flat-top peak placed on the remarkably long i = 2 plateau. This anomalous i = 1 peak separates two different regimes: (i) a traditional QHE at relatively low fields corresponding to a small density of mobile holes p(s) and (ii) a high-field QHE with a 2-1 plateau-plateau transition corresponding to a much larger p(s). The high-field part is strongly sensitive to external influences such as gate voltages, in contrast to the low-field part, which is much less responsive. We explain the observed behavior by analyzing the calculated trajectories of the Fermi level E-F(B) between hole-like and electron-like Landau levels (LLs). At low fields, E-F is captured by the lateral maximum (LM) of the valence subband, and only holes in the center of the Brillouin zone contribute to QHE, while holes in the LM are inactive. In contrast, at fields above the reentry, E-F rises significantly higher than LM, approaching the zero-mode LLs, and all holes come into play in QHE. At intermediate fields, the reentrance is caused by a combination of two factors in the specific energy spectrum of this DQW: (i) the superposition of an electron-like LL on hole-like LLs and (ii) the stabilizing influence of the LM reservoir on E-F(B).

We present the results of a comparative analysis of the magnetocaloric effect (MCE) in Pr0.7Sr0.2Ca0.1MnO3, through direct and indirect measurements, using experimentally measured magnetization, specific heat, magnetostriction, resistivity, thermal diffusivity and thermal conductivity parameters. We have demonstrated that the change in each parameter in response to a magnetic field near the ferromagnetic-paramagnetic phase transition temperature of the material correlates with the change in magnetic entropy. These findings allow us to interrelate these parameters and provide an alternative, effective approach for accessing the usefulness of magnetocaloric materials.