The contribution of the electron-electron interaction to conductivity is analyzed step by step starting from the high conductivity in gated GaAs/In x Ga 1Ϫx As/GaAs heterostructures with different starting disorders. We demonstrate that the diffusion theory works down to k F lӍ1.5Ϫ2, where k F is the Fermi quasimomentum and l is the mean free path. It is shown that the e-e interaction gives smaller contribution to the conductivity than the interference independent of the starting disorder, and its role rapidly decreases with decreasing k F l.Quantum corrections to the conductivity in disordered metals and doped semiconductors have been intensively studied since 1980. 1 Two mechanisms led to these corrections: ͑i͒ the interference of the electron waves propagating in opposite directions along closed paths; ͑ii͒ electronelectron (e-e) interaction. The interference decreases the conductivity and its role increases with decreasing temperature. Behavior of the e-e contribution to the conductivity strongly depends on value of k B T/ប, where is transport relaxation time, and Fermi liquid interaction parameter F 0 . 2,3 It dramatically changes at crossover from the diffusion regime (k B T/បӶ1) to the ballistic one (k B T/បտ1) and can lead to inversion of sign of the temperature dependence of the conductivity. In addition, in the ballistic regime the e-e contribution depends on scale of scattering potential. The interaction correction for pointlike scattering potential was considered in Refs. 2 and 3 and for the long-range potential was studied theoretically in Ref. 4 and experimentally in Ref. 5. In this paper we track the evolution of the interaction correction as the conductivity decreases. Because the absolute value of both interference and interaction corrections increases with decreasing temperature, they determine in large part the low-temperature transport in two-dimensional ͑2D͒ systems in this case. The interference or weaklocalization ͑WL͒ correction ␦ WL is proportional to Ϫln( /), where is the phase relaxation time, ϰT Ϫp , pӍ1 in dirty limit. The correction due to the e-e interaction ␦ ee is proportional to Ϫln͓ប/(k B T)͔ in the diffusion regime. 1 It immediately follows that at increasing disorder, i.e., at decreasing , both corrections have to be enhanced in absolute value and can become comparable with the Drude conductivity. In this case the low-temperature conductivity will be significantly less than the Drude conductivity, and the strong temperature dependence of the conductivity has to appear. On further increase of disorder the transition to the hopping conductivity has to occur.All theories of quantum corrections for both diffusive 1 and ballistic 2-4 regimes were developed for the case k F l ӷ1, where k F and l are the Fermi quasimomentum and the classical mean free path, respectively. Under this condition the quantum corrections to the conductivity are small in magnitude compared with the Drude conductivity 0 ϭk F lG 0 with G 0 ϭe 2 /(2 2 ប) at any accessible temperature. With decreasing k F l ...

Weak antilocalization is studied in an InGaAs quantum well. Anomalous magnetoresistance is measured and described theoretically in fields perpendicular, tilted and parallel to the quantum well plane. Spin and phase relaxation times are found as functions of temperature and parallel field. It is demonstrated that spin dephasing is due to the Dresselhaus spin-orbit interaction. The values of electron spin splittings and spin relaxation times are found in the wide range of 2D density. Application of in-plane field is shown to destroy weak antilocalization due to competition of Zeeman and microroughness effects. Their relative contributions are separated, and the values of the in-plane electron g-factor and characteristic size of interface imperfections are found.Comment: 8 pages, 8 figure

Results of detailed investigations of the conductivity and Hall effect in gated single quantum well GaAs/InGaAs/GaAs heterostructures with two-dimensional electron gas are presented. A successive analysis of the data has shown that the conductivity is diffusive for kF l = 25 − 2. The absolute value of the quantum corrections for kF l = 2 at low temperature is not small, e.g., it is about 70 % of the Drude conductivity at T = 0.46 K. For kF l = 2 − 0.5 the conductivity looks like diffusive one. The temperature and magnetic field dependences are qualitatively described within the framework of the self-consistent theory by Vollhardt and Wölfle. The interference correction is therewith close in magnitude to the Drude conductivity so that the conductivity σ becomes significantly less than e 2 /h. We conclude that the temperature and magnetic field dependences of conductivity in the whole kF l range are due to changes of quantum corrections.

The results of an experimental study of the energy spectrum of the 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. The comparison with the 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.

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