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The electron properties of artificially disordered superlattices embedded in a wide AlGaAs parabolic well were investigated in a strong magnetic field. We demonstrated that in the extreme quantum limit the interlayer disorder results in formation of a new correlated phase. A nearly uniform electron distribution over the superlattice wells was found in a weak magnetic field. However, a nonuniform phase with partially localized electrons, representing well-developed fractional quantum Hall effect features, was observed in high magnetic field (at the filling factor ν < 1). A distinct magnetic field-induced transition separates these two phases. [ABSTRACT FROM AUTHOR]

Abstract: Magneto-capacitance was studied in narrow miniband GaAs/AlGaAs superlattices where quasi-two dimensional electrons revealed the integer quantum Hall effect. The interwell tunneling was shown to reduce the effect of the quantization of the density of states on the capacitance of the superlattices. In such case the minimum of the capacitance observed at the filling factor was attributed to the decrease of the electron compressibility due to the formation of the incompressible quantized Hall phase. In accord with the theory this phase was found strongly inhomogeneous. The incompressible fraction of the quantized Hall phase was demonstrated to rapidly disappear with the increasing temperature. [Copyright &y& Elsevier]

Abstract: The artificial random Gaussian-type potential built in the GaAs/AlGaAs superlattices grown by molecular beam epitaxy was explored by various methods. The effect of the intentional disorder was shown to dominate intrinsic superlattice imperfections and its impact on the electronic properties was found to be in good agreement with the theoretical predictions. It was demonstrated that the modern state of the molecular beam epitaxy allows for a growth of the superstructured materials with well-defined disorder strength. [Copyright &y& Elsevier]

The capacitance–voltage characteristics of (GaAs)m/(AlAs)n superlattices and of a GaAs/AlGaAs multiple quantum well system were used as a tool to probe the homogeneity of the studied samples. Evidences of a strong electron localization in the superlattices even with the presence of minibands were found. We interpret this result taking into account the presence of local inhomogeneities in the superlattices which causes the breakdown of the coherence of the miniband transport and therefore, give rise to the electron localization. In order to support this conclusion we numerically calculate the capacitance of the superlattices assuming a localization center near the region where electron confinement takes place and the results were found in good agreement with the measured capacitance. [Copyright &y& Elsevier]