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Öğe The current polarization rectification of the integer quantized Hall effect(Elsevier Science Bv, 2010) Eksi, D.; Kilicoglu, O.; Aktas, S.; Siddiki, A.We report on our theoretical investigation considering the widths of quantized Hall plateaus (QHPs) depending on the density asymmetry induced by the large current within the out-of-linear response regime. We solve the Schrodinger equation within the Hartree type mean field approximation using Thomas-Fermi-Poisson nonlinear screening theory. We observe that the two-dimensional electron system splits into compressible and incompressible regions for certain magnetic field intervals, where the Hall resistance is quantized and the longitudinal resistance vanishes, if an external current is imposed. We found that the strong current imposed induces an asymmetry on the widths of the incompressible strips (ISs) depending linearly on the current intensity and can be balanced by an inhomogeneous donor distribution. (C) 2009 Elsevier B.V. All rights reserved.Öğe Investigation of the coupling asymmetries at double-slit interference experiments(Iop Publishing Ltd, 2010) Mese, A. I.; Bilekkaya, A.; Arslan, S.; Aktas, S.; Siddiki, A.Double-slit experiments inferring the phase and the amplitude of the transmission coefficient performed at quantum dots (QDs), in the Coulomb blockade regime, present anomalies at the phase changes depending on the number of electrons confined. This phase change cannot be explained if one neglects the electron-electron interactions. Here, we present our numerical results, which simulate the real sample geometry by solving the Poisson equation in 3D. The screened potential profile is used to obtain energy eigenstates and eigenvalues of the QD. We find that, certain energy levels are coupled to the leads stronger compared to others. Our results give strong support to the phenomenological models in the literature describing the charging of a QD and the abrupt phase changes.Öğe Modeling of quantum point contacts in high magnetic fields and with current bias outside the linear response regime(Amer Physical Soc, 2008) Arslan, S.; Cicek, E.; Eksi, D.; Aktas, S.; Weichselbaum, A.; Siddiki, A.The electron and current-density distributions in the close proximity of quantum point contacts (QPCs) are investigated. A three-dimensional Poisson equation is solved self-consistently to obtain the electron density and potential profile in the absence of an external magnetic field for gate and etching defined devices. We observe the surface charges and their apparent effect on the confinement potential, when considering the (deeply) etched QPCs. In the presence of an external magnetic field, we investigate the formation of the incompressible strips and their influence on the current distribution both in the linear response and out of linear response regime. A spatial asymmetry of the current carrying incompressible strips, induced by the large source drain voltages, is reported for such devices in the nonlinear regime.Öğe Screening model of metallic nonideal contacts in the integer quantized Hall regime(Amer Physical Soc, 2010) Eksi, D.; Kilicoglu, O.; Goektas, O.; Siddiki, A.In this work, we calculate the electron and the current-density distributions both at the edges and the bulk of a two-dimensional electron system, focusing on ideal and nonideal contacts. A three-dimensional Poisson equation is solved self-consistently to obtain the potential profile in the absence of an external magnetic field considering a Hall bar defined both by gates (contacts) and etching (lateral confinement). In the presence of a perpendicular magnetic field, we obtain the spatial distribution of the incompressible strips, taking into account the electron-electron interactions within the Thomas-Fermi approximation. Using a local version of Ohm's law, together with a relevant conductivity model, we also calculate the current distribution. We observe that the incompressible strips can reside either on the edge or at the bulk depending on the field strength. Our numerical results show that, due to a density poor region just in front of the contacts, the incompressible strips are not in direct contact with the injection region when considering nonideal contact configuration. Such a nonideal contact is in strong contrast with the conventional edge channel pictures, hence has a strong influence on transport. We also take into account heating effects in a phenomenological manner and propose a current injection mechanism from the compressible regions to the incompressible regions. The model presented here perfectly agrees with the local probe experiments all together with the formation of hot-spots.Öğe Spatial distribution of the incompressible strips at AB interferometer(Elsevier Science Bv, 2010) Cicek, E.; Mese, A. I.; Ulas, M.; Siddiki, A.In this work, the edge physics of an Aharonov-Bohm interferometer (ABI) defined on a two dimensional electron gas, subject to strong perpendicular magnetic field B, is investigated. We solve the three dimensional Poisson equation using numerical techniques starting from the crystal growth parameters and surface image of the sample. The potential profiles of etched and gate defined geometries are compared and it is found that the etching yields a steeper landscape. The spatial distribution of the incompressible strips is investigated as a function of the gate voltage and applied magnetic field, where the imposed current is confined to. AB interference is investigated due to scattering processes between two incompressible edge-states. (C) 2009 Elsevier B.V. All rights reserved.Öğe Theoretical investigation of the effect of sample properties on the electron velocity in quantum Hall bars(Amer Physical Soc, 2007) Eksi, D.; Cicek, E.; Mese, A. I.; Aktas, S.; Siddiki, A.; Hakioglu, T.We report on our theoretical investigation of the effects of the confining potential profile and sample size on the electron velocity distribution in (narrow) quantum Hall systems. The electrostatic properties of the electron system are obtained by the Thomas-Fermi-Poisson nonlinear screening theory. The electron velocity distribution as a function of the lateral coordinate is obtained from the slope of the screened potential at the Fermi level and within the incompressible strips. We compare our findings with the recent experiments.Öğe Theoretical investigation of the electron velocity in quantum Hall bars, in the out of linear response regime(Elsevier, 2008) Siddiki, A.; Eksi, D.; Cicek, E.; Mese, A. I.; Aktas, S.; Hakioglu, T.We report on our theoretical investigation of the electron velocity in (narrow) quantum Hall systems, considering the out-of-linear-response regime. The electrostatic properties of the electron system are obtained by the Thomas-Fermi-Poisson nonlinear screening theory. The electron velocity distribution as a function of the lateral coordinate is obtained from the slope of the screened potential within the incompressible strips (ISs). The asymmetry induced by the imposed current on the ISs is investigated, as a function of the current intensity and impurity concentration. We find that the width of the IS on one side of the sample increases linearly with the intensity of the applied current and decreases with the impurity concentration. (C) 2007 Elsevier B.V. All rights reserved.Öğe Time-dependent transport in Aharonov-Bohm interferometers(Iop Publishing Ltd, 2012) Kotimaki, V.; Cicek, E.; Siddiki, A.; Rasanen, E.A numerical approach is employed to explain transport characteristics in realistic, quantum Hall-based Aharonov-Bohm (AB) interferometers. Firstly, the spatial distribution of incompressible strips, and thus the current channels, are obtained by applying a self-consistent Thomas-Fermi method to a realistic heterostructure under quantized Hall conditions. Secondly, the time-dependent Schrodinger equation is solved for electrons injected in the current channels. Distinctive AB oscillations are found as a function of the magnetic flux. The oscillation amplitude strongly depends on the mutual distance between the transport channels and on their width. At an optimal distance the amplitude and thus the interchannel transport is maximized, which determines the maximum visibility condition. On the other hand, the transport is fully suppressed at magnetic fields corresponding to half-integer flux quanta. The results confirm the applicability of realistic AB interferometers as controllable current switches.Öğe Where are the edge-states near the quantum point contacts? A self-consistent approach(Elsevier, 2008) Siddiki, A.; Cicek, E.; Eksi, D.; Mese, A. I.; Aktas, S.; Hakioglu, T.In this work, we calculate the current distribution, in the close vicinity of the quantum point contacts (QPCs), taking into account the Coulomb interaction. In the first step, we calculate the bare confinement potential of a generic QPC and, in the presence of a perpendicular magnetic field, obtain the positions of the incompressible edge states (IES) taking into account electron-electron interaction within the Thomas-Fermi theory of screening. Using a local version of Ohm's law, together with a relevant conductivity model, we also calculate the current distribution. We observe that, the imposed external current is confined locally into the incompressible strips. Our calculations demonstrate that, the inclusion of the electron-electron interaction, strongly changes the general picture of the transport through the QPCs. (C) 2007 Elsevier B.V. All rights reserved.
