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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 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