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Исследованы особенности локального транспорта в одно и квазиодномерных структурах методом измерения магнитотранспорта в присутствии сканирующего затвора атомносилового микроскопа (scanning gate microscopy). Продемонстрировано влияние волн зарядовой плотности, а также прозрачности потенциальных барьеров вблизи интерфейса металлполупроводник на электронный транспорт в нанопроволоках InAs. Кроме того, показана возможность измерения спектроскопии и работы выхода в углеродной нанотрубке при измерении топографии в режиме тэппинга.

The spin splitting of conduction band electrons in inversion-asymmetric InGaAs/InP quantum wells is studied by Shubnikov-de Haas measurements combining the analysis of beating patterns and coincidence measurements in doubly tilted magnetic fields. The method allows us to determine the absolute values of the Rashba and linear Dresselhaus spin-orbit interaction coefficients, their relative sign and the full Land\'e g-tensor. This is achieved by analyzing the anisotropy of the beat node positions with respect to both polar and azimuthal angles between the magnetic field direction and the quantum well normal. We show that the spin-orbit interaction is dominated by a large Rashba coefficient together with a linear Dresselhaus coefficient that is 10 $\%$ of the Rashba coefficient. Their relative sign is found to be positive. The g-tensor is found to have a marked out-of-plane anisotropy and a smaller but distinct in-plane anisotropy due to spin-orbit interaction.

We investigate the correlations of mutual positions of charge density waves nodes in side-by-side placed InAs nanowires in presence of a conductive atomic force microscope tip served as a mobile gate at helium temperatures. Scanning gate microscopy scans demonstrate mutual correlation of positions of charge density waves nodes of two wires. A general mutual shift of the nodes positions and "crystal lattice mismatch" defect were observed. These observations demonstrate the crucial role of Coulomb interaction in formation of charge density waves in InAs nanowires.

We performed measurements at helium temperatures of the electronic transport in an InAs quantum wire ($R_{wire} \sim 30$\,k$\Omega$) in the presence of a charged tip of an atomic force microscope serving as a mobile gate. The period and the amplitude of the observed quasiperiodic oscillations are investigated in detail as a function of electron concentration in the linear and non-linear regime. We demonstrate the influence of the tip-to-sample distance on the ability to locally affect the top subband electrons as well as the electrons in the disordered sea. Furthermore, we introduce a new method of detection of the subband occupation in an InAs wire, which allows us to evaluate the number of the electrons in the conductive band of the wire.

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We study the magnetotransport in small hybrid junctions formed by high-mobility GaInAs/InP heterostructures coupled to superconducting (S) and normal metal (N) terminals. Highly transmissive superconducting contacts to a two-dimensional electron gas (2DEG) located in a GaInAs/InP heterostructure are realized by using a Au/NbN layer system. The magnetoresistance of the S/2DEG/N structures is studied as a function of dc bias current and temperature. At bias currents below a critical value, the resistance of the S/2DEG/N structures develops a strong oscillatory dependence on the magnetic field, with an amplitude of the oscillations considerably larger than that of the reference N/2DEG/N structures. The experimental results are qualitatively explained by taking Andreev reflection in high magnetic fields into account., 5 pages, 5 figures

The magnetotransport in a set of identical parallel AlxGa1-xN/GaN quantum wire structures is investigated. The width of the wires ranges between 1110 and 340 nm. For all sets of wires, clear Shubnikov-de Haas oscillations are observed. We find that the electron concentration and mobility are approximately the same for all wires, confirming that the electron gas in the AlxGa1-xN/GaN heterostructure is not deteriorated by the fabrication procedure of the wire structures. For the wider quantum wires, the weak antilocalization effect is clearly observed, indicating the presence of spin-orbit coupling. For narrow quantum wires with an effective electrical width below 250 nm, the weak antilocalization effect is suppressed. By comparing the experimental data to a theoretical model for quasi-one-dimensional structures, we come to the conclusion that the spin-orbit scattering length is enhanced in narrow wires.

We study the magnetotransport in small hybrid junctions formed by high-mobility GaxIn1-xAs/InP heterostructures coupled to superconducting (S) and normal metal (N) terminals. Highly transmissive superconducting contacts to a two-dimensional electron gas (2DEG) located in a GaxIn1-xAs/InP heterostructure are realized by using a Au/NbN layer system. The magnetoresistance of the S/2DEG/N structures is studied as a function of dc bias current and temperature. At bias currents below a critical value, the resistance of the S/2DEG/N structures develops a strong oscillatory dependence on the magnetic field, with an amplitude of the oscillations considerably larger than that of the reference N/2DEG/N structures. The experimental results are qualitatively explained by taking into account Andreev reflection in high magnetic fields.

We studied the suppression of weak antilocalization in an AlxGa1-xN/GaN two-dimensional electron gas in the presence of an additional in-plane magnetic field. By comparing our experimental data to a theoretical model, we concluded that the suppression can be attributed mainly to the Zeeman effect, while the contribution due to disorder at the AlxGa1-xN/GaN heterointerface is considerably smaller. Furthermore, our results give further evidence for the value of spin-orbit scattering length determined from weak antilocalization measurements.

The magnetotransport in a set of identical parallel AlGaN/GaN quantum wire structures was investigated. The width of the wires was ranging between 1110 nm and 340 nm. For all sets of wires clear Shubnikov--de Haas oscillations are observed. We find that the electron concentration and mobility is approximately the same for all wires, confirming that the electron gas in the AlGaN/GaN heterostructure is not deteriorated by the fabrication procedure of the wire structures. For the wider quantum wires the weak antilocalization effect is clearly observed, indicating the presence of spin-orbit coupling. For narrow quantum wires with an effective electrical width below 250 nm the weak antilocalization effect is suppressed. By comparing the experimental data to a theoretical model for quasi one-dimensional structures we come to the conclusion that the spin-orbit scattering length is enhanced in narrow wires., Comment: 6 pages, 5 figures

We have studied the spin-orbit interaction in a high mobility two-dimensional electron gas in a GaInAs/InP heterostructure as a function of an applied gate voltage as well as a function of temperature. Highly sensitive magnetotransport measurements of weak antilocalization as well as measurements of Shubnikov-de Haas oscillations were performed in a wide range of electron sheet concentrations. In our samples, the electron transport takes place in the strong spin precession regime in the whole range of applied gate voltages, which is characterized by the spin precession length being shorter than the elastic mean free path. The magnitude of the Rashba spin-orbit coupling parameter was determined by fitting the experimental curves by a simulated quantum conductance correction according to a model proposed recently by Golub [Phys. Rev. B 71, 235310 (2005)]. A comparison of the Rashba coupling parameter extracted using this model with the values estimated from the analysis of the beating pattern in the Shubnikov-de Haas oscillations showed a good agreement.

The magnetoconductivity of GaxIn1-xAs/InP quantum wires with widths in the range of 1220-250 nm was investigated. The finite zero-field spin splitting in our samples gives rise to spin relaxation and weak antilocalization in wide wires. In contrast, for the narrow wires, only weak-localization behavior is seen even though the zero-field spin splitting is independent of wire width. The observed renormalization of the spin-relaxation length due to purely geometrical effects can be described quantitatively using a model where the effect of spin precession is represented by spin-dependent pseudomagnetic fluxes, and by exact numerical transport calculations.

Weak antilocalization and the Shubnikov-de Haas effect were investigated in AlxGa1-xN/GaN two-dimensional electron gases. The weak antilocalization measurements on a gated sample revealed a constant spin-orbit scattering length, which does not change if the Al content or the thickness of the AlxGa1-xN barrier layer is varied. The occurrence of spin-orbit coupling is assigned to the lack of crystal inversion symmetry. Although for some of the samples a beating pattern was observed in the Shubnikov-de Haas oscillations, its presence was not attributed to spin-orbit coupling but rather to inhomogeneities in the AlxGa1-xN barrier.

The effect of electron cyclotron resonance plasma cleaning on the contact resistance between a superconducting Nb layer and a two-dimensional electron gas in a strained InxGa1-xAs/InP heterostructure is investigated. Cleaning by a He/H plasma results in a rough semiconductor surface and a high interface resistance. In contrast, by using a pure He plasma a smooth semiconductor surface with a considerably lower interface resistance is obtained. (C) 2000 American Institute of Physics. [S0021-8979(00)10119-7].

We report on the magnetization of ensembles of etched quantum dots with a lateral diameter of 460 nm, which we prepared from InGaAs/InP heterostructures. The quantum dots exhibit 1/B-periodic de-Haas–van-Alphen-type oscillations in the magnetization M(B) for external magnetic fields B > 2 T, measured by torque magnetometry at 0.3 K. We compare the experimental data to model calculations assuming different confinement potentials and including ensemble broadening effects. The comparison shows that a hard wall potential with an edge depletion width of 100 nm explains the magnetic behavior. Beating patterns induced by Rashba spin–orbit interaction (SOI) as measured in unpatterned and nanopatterned InGaAs/InP heterostructures are not observed for the quantum dots. From our model we predict that signatures of SOI in the magnetization could be observed in larger dots in tilted magnetic fields.