Abstract. We have measured the temperature (0.1 ≤ T ≤ 15 K) and magnetic field (0 ≤ B ≤ 32 T) dependences of longitudinal and Hall resistivities for the p-Ge0.93Si0.07/Ge multilayers with different Ge layer widths 10 ≤ dw ≤ 38 nm and hole densities ps = (1÷5)·10 15 m -2 . An extremely high sensitivity of the experimental data (the structure of magnetoresistance traces, relative values of the inter-Landau-level (LL) gaps deduced from the activated magnetotransport etc) to the quantum well (QW) characteristics has been revealed in the cases when the Fermi level reached the second confinement subband. The background density of states (5÷10)·10 14 m -2 meV -1 deduced from the activation behavior of the magnetoresistance was too high to be attributed to the LL tails, but may be accounted for within a smooth random potential model. The hole gas in the Ge quantum well was found to separate into two sublayers for dw > ~35 nm and ps ≈ 5·10 15 m -2 . Concomitantly the positive magnetoresistance emerged in the weakest fields, from which different mobilities in the sublayers were deduced. A model is suggested to explain the existence of the plateaux close to the fundamental values in a system of two parallel layers with different mobilities.
The article presents the experimental results concerning the role of cobalt impurities in low tem perature electrical conduction and in the Hall concentration of electrons in crystals of mercury selenide. In the limit of small concentrations of the impurities, a slow variation of the electron concentration was found as a function of impurity content, which can correspond to a donor character of the impurity d levels of cobalt atoms located in the conduction band of the host crystal under conditions of hybridization. Characteristic features have been observed in the concentration and temperature dependences of the electrical conductivity, similar to those that manifest themselves in crystals with hybridized states of iron impurities. As a result, the set of data obtained on crystals with cobalt impurities, including the previously published data on the concen tration dependence of the Curie constant and on the temperature dependence of thermopower, can be used on a qualitative level as an experimental substantiation of the previously predicted existence of two donor hybridized electron states of a cobalt impurity atom in the conduction band.
We have measured the temperature (0.1 T 15 K) and magnetic field (0 B 12 T) dependences of longitudinal and Hall resistivities for p-Ge 0.93 Si 0.07 /Ge multilayers with different Ge layer widths 10 d w 38 nm and hole densities p s =(1-5)×10 15 m −2 . Two models for the long-range random impurity potential (the model with randomly distributed charged centres located outside the conducting layer and the model of the system with a spacer) are used for evaluation of the impurity potential fluctuation characteristics: the random potential amplitude, nonlinear screening length in the vicinity of integer filling factors (FFs) ν = 1 and 2 and the background density of states (DOS). The described models are suitable for an explanation of the unusually high value of DOS at ν = 1 and 2, in contrast to the short-range impurity potential models. For half-integer FFs the linear temperature dependence of the effective quantum Hall effect (QHE) plateau-to-plateau transition width ν 0 (T ) is observed in contrast to scaling behaviour for systems with short-range disorder. The finite T → 0 width of QHE transitions may be due to an effective low-temperature screening of smooth random potential owing to Coulomb repulsion of electrons.
A theoretical description is given of the concentration dependence of the g factor of the conduction electrons in hybridized states on donor impurities in a semiconductor taking account of the effect of the interelectronic interaction within the framework of the Fermi-liquid approach. It is shown that the theoretically predicted dependence due to the Fermi-liquid interaction is non-monotonic in the resonance interval because of partial electron localization on impurities.
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