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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 results of an experimental study of the energy spectrum of a valence band in a HgTe quantum well of width d < 6.3 nm with normal spectrum in the presence of a strong spin-orbit splitting are reported. The analysis of the temperature, magnetic field, and gate voltage dependences of the Shubnikov-de Haas oscillations allows us to restore the energy spectrum of the two valence-band branches, which are split by the spin-orbit interaction. Comparison with a theoretical calculation shows that a six-band kP theory well describes all the experimental data in the vicinity of the top of the valence band. [ABSTRACT FROM AUTHOR]

The results of an experimental study of the magnetoresistivity and the Hall and Shubnikov-de Haas effects for a heterostructure with a HgTe quantum well of 20.2 nm width are reported. The measurements were performed on gated samples over a wide range of electron and hole densities including the vicinity of a charge neutrality point. Analyzing the data, we conclude that the electron and hole energy spectra are in qualitative agreement with those calculated within the framework of kP model. The electron and hole subbands are overlapped due to the nonmonotonic dispersion of the hole subband resulting in a semimetallic state. The main result of the paper, however, is the drastic quantitative difference in the experimental and calculated spectra of the hole subband. So, the hole effective mass found from the analysis of the Shubnikov-de Haas oscillations is positive and equal to approximately 0.2m0 and practically independent of the quasimomentum (k) starting from k2 ≃0.7 × 1012 cm2, while the theory predicts negative (electronlike) effective mass up to k2 ≃ 6 × 1012 cm2. The experimental effective mass near k = 0, where the hole energy spectrum is electronlike, is close to -0.005m0, whereas the theoretical value is about -0.1m0. [ABSTRACT FROM AUTHOR]

The results of an experimental study of the magnetoconductivity of two-dimensional (2D) electron gas caused by suppression of the interference quantum correction in a HgTe single quantum well heterostructure with an inverted energy spectrum are presented. It is shown that only the antilocalization magnetoconductivity is observed at relatively high conductivity, σ > (20-30) G0, where G0 = e2/2π2ħ. The antilocalization correction demonstrates a crossover from 0.5 In (τφ/τ) to 1.0 In (τφ/τ) behavior with increasing conductivity (here τφ and τ are the phase relaxation and transport relaxation times, respectively). It is interpreted as a result of crossover to the regime when the two chiral branches of the electron energy spectrum independently contribute to the weak antilocalization. At lower conductivity, σ < (20-30) G0, the magnetoconductivity behaves similarly to that in usual 2D systems with fast spin relaxation: It is negative in low magnetic fields and positive in higher ones. We have found that the temperature dependences of the fitting parameter τφ corresponding to the phase relaxation time demonstrate reasonable behavior, close to 1/T, over the whole conductivity range from 5 G0 up to 130 G0. However, the τφ value remains practically independent of conductivity, in contrast to conventional 2D systems with simple energy spectra, in which τφ is enhanced with conductivity. [ABSTRACT FROM AUTHOR]

The electron-electron interaction quantum correction to the conductivity of the gated single quantum well InP/Ino.53Gao.47 As heterostructures is investigated experimentally. The analysis of the temperature and magnetic field dependences of the conductivity tensor allows us to obtain the diffusion part of the interaction correction for different values of spin-relaxation rate, 1 /τs. The surprising result is that the spin-relaxation processes do not suppress the interaction correction in the triplet channel and thus do not enhance the correction in magnitude contrary to theoretical expectations even in the case of relatively fast spin relaxation, 1 / Tτs ≃ (20 -- 25) > 1. [ABSTRACT FROM AUTHOR]

The electron-electron interaction quantum correction to the conductivity of the gated double well AlxGa1-xAs/GaAs structures is investigated experimentally. The analysis of the temperature and magnetic field dependences of the conductivity tensor allows us to obtain reliably the diffusion part of the interaction correction for the regimes when the structure is balanced (i.e., for equal electron concentrations in the wells) and when only one quantum well is occupied. The surprising result is that the interaction correction does not reveal resonant behavior: it is practically the same for both regimes. [ABSTRACT FROM AUTHOR]

The results of experimental study of the weak localization phenomenon in 2D system with artificial inhomogeneity of potential relief are presented. It is shown that the shape of the magnetoconductivity curve is determined by the statistics of closed paths. The area distribution function of closed paths has been obtained using the Fourier transformation of the magnetoconductivity curves taken at different temperatures. The experimental results are found in a good agreement with the results of computer simulation. [ABSTRACT FROM AUTHOR]

Effect of the magnetic field on the rate of phase breaking is studied. It is shown that the magnetic field resulting in the decrease of phase relaxation rate $\tau_{\phi}^{-1}$ makes the negative magnetoresistance due to suppression of the electron interference to be smoother in shape and lower in magnitude than that found with constant $\tau_{\phi}^{-1}$-value. Nevertheless our analysis shows that experimental magnetoconductance curves can be well fitted by the Hikami–Larkin–Nagaoka expression.1 The fitting procedure gives the value of τ/τϕ, where τ is the quasi-momentum relaxation time, which is close to the value of τ/τϕ(B = 0) with an accuracy of 25% or better when the temperature varies within the range from 0.4 to 10 K. The value of the prefactor α found from this procedure lies within the interval 0.9–1.2. [ABSTRACT FROM AUTHOR]

The interference quantum correction to the conductivity and its temperature and magnetic-field dependence with taking into account the spin relaxation processes is investigated. The results of numerical and real physical experiments are reported. We show that the shape of the magnetoresistance is nonuniversal beyond the diffusion regime, when the close trajectories with small number of collisions are of importance. It is sensitive to anisotropy of scattering and correlation of impurity distribution. [ABSTRACT FROM AUTHOR]

The energy spectrum of the valence band in HgTe/CdxHg1-xTe quantum wells of a width (8-20) nm has been studied experimentally by magnetotransport effects and theoretically in the framework of a four-band kP method. Comparison of the Hall density with the density found from a period of the Shubnikov-de Haas (SdH) oscillations clearly shows that the degeneracy of states of the top of the valence band is equal to 2 at the hole density p<5.5×1011cm-2. Such degeneracy does not agree with the calculations of the spectrum performed within the framework of the four-band kP method for symmetric quantum wells. These calculations show that the top of the valence band consists of four spin-degenerate extremes located at k≠0 (valleys) which gives the total degeneracy K=8. It is shown that taking into account the "mixing of states" at the interfaces leads to the removal of the spin degeneracy that reduces the degeneracy to K=4. Accounting for any additional asymmetry, for example, due to the difference in the mixing parameters at the interfaces, the different broadening of the boundaries of the well, etc., leads to reduction of the valleys degeneracy, making K=2. It is noteworthy that for our case twofold degeneracy occurs due to degeneracy of two single-spin valleys. The hole effective mass (mh) determined from analysis of the temperature dependence of the amplitude of the SdH oscillations shows that mh is equal to (0.25±0.02)m0 and weakly increases with the hole density. Such a value of mh and its dependence on the hole density are in a good agreement with the calculated effective mass. [ABSTRACT FROM AUTHOR]

Energy spectra both of the conduction and valence bands of the HgTe quantum wells with a width close to the Dirac point were studied experimentally. Simultaneous analysis of the Shubnikov-de Haas oscillations and the Hall effect over a wide range of electron and hole densities yields surprising results: the top of the valence band is strongly split by spin-orbit interaction while the splitting of the conduction band is absent, within experimental accuracy. This holds true for the structures with normal and inverted band ordering. The results obtained are inconsistent with the results of kP calculations, in which the smooth electric field across the quantum well is only reckoned in. It is shown that taking into account the asymmetry of the quantum-well interfaces within a tight-binding method gives reasonable agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The nonohmic conductivity of two-dimensional hole gas (2DHG) in single GaAsIn0.2Ga0.8AsGaAs quantum-well structures within the temperature range of 1.4-4.2 K, the carrier's densities p=(1.5-8)x1015m-2 and a wide range of conductivities (10-4-100)G0 (G0=e²/π h) was investigated. It was shown that at conductivity σ>G0 the energy relaxation rate P(Th,TL) is well described by the conventional theory P. J. Price J. Appl. Phys. 53 6863 (1982) , which takes into account scattering on acoustic phonons with both piezoelectric and deformational potential coupling to holes. At the conductivity range 0.01G0<σ