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Öğe Binding energy of a hydrogenic impurity in a coaxial quantum wire with an insulator layer(Academic Press Ltd- Elsevier Science Ltd, 2017) Kes, H.; Bilekkaya, A.; Aktas, S.; Okan, S. E.The electronic properties of a coaxial cylindrical quantum well-barrier system constituted about an central insulating wire were determined under an external electric field. The model wire, inside to outside, was considered to be layered as AlAs/GaAs/Alx1Ga1-xAs/GaAs/Alx2Ga1-x2As. Within the framework of the effective mass approximation, the binding energy of a hydrogenic impurity is calculated by using the combination of the fourth-order Runge-Kutta method and variational approaches. The binding energy exhibits sharp changes depending on the impurity position and the geometrical parameters of the structure such as the well widths of the GaAs wires and the height and thickness of the barrier constituted by Alx1Ga1-x1 As. The binding energy of the electron was found to be independent from the impurity position for the specific widths of the well wires. Also, the barrier properties appeared as very effective parameters in controlling the probability distribution of the electron. (C) 2017 Elsevier Ltd. All rights reserved.Öğe Condensation of two-dimensional harmonically confined bosons with Bessel-type interactions(Amer Physical Soc, 2011) Mese, A. I.; Capuzzi, P.; Aktas, S.; Akdeniz, Z.; Okan, S. E.We study the ground-state configurations of few interacting bosons confined in two dimensions by anisotropic harmonic potentials. By means of variational calculations, including correlation effects, we show that the arrangement of bosons strongly depends on the strength of the repulsive interaction and the anisotropy of the confinement. We compute the condensate fraction of the system and found that by increasing the anisotropy of the potential a weaker interaction suffices to destroy the condensate and favors the emergence of a crystal-like structure.Öğe Control of a resonant tunneling structure by intense laser fields(Academic Press Ltd- Elsevier Science Ltd, 2016) Aktas, S.; Kes, H.; Boz, F. K.; Okan, S. E.The intense laser field effects on a resonant tunneling structure were studied using computational methods. The considered structure was a GaAs/InxGa1-xAs/Al0.3Ga0.7As/InyGa1-yAs/AlAs/GaAs well-barrier system. In the presence of intense laser fields, the transmission coefficient and the dwell time of the structure were calculated depending on the depth and the width of InGaAs wells. It was shown that an intense laser field provides full control on the performance of the device as the geometrical restrictions on the resonant tunneling conditions overcome. Also, the choice of the resonant energy value becomes possible depending on the field strength. (C) 2016 Elsevier Ltd. All rights reserved.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 The Effect on the Optical Absorption Coefficients due to the Positions in the Plane of Square GaAs/Al(GaAs) Quantum Well Wire under the Laser Field(Polish Acad Sciences Inst Physics, 2019) Bekar, B.; Boz, F. K.; Aktas, S.; Okan, S. E.The laser field effects on the electronic and optical properties depending on two different positions in the plane of GaAs/Al (GaAs) quantum wire with square cross sections have been investigated. The electron energy levels and the electronic wave functions of the wires are calculated using the finite differences method within the effective mass approximation. The differences of the total absorption coefficients and the reflection index changes sourced from the cross-sectional shape were determined and explained with and without laser field. From the results the blue shift and red shift effects on the total absorption coefficients and the reflection index changes were identified depending on the laser field strength and the positions of square GaAs/Al(GaAs) quantum well wire in the plane.Öğe Electric and magnetic field effects on the binding energy of a hydrogenic impurity in quantum well wires with different shapes(Academic Press Ltd- Elsevier Science Ltd, 2008) Bilekkaya, A.; Aktas, S.; Okan, S. E.; Boz, F. K.In this work, we directly calculate the ground state energies for an electron in quantum well wires (QWWs) with different shapes in the presence of applied electric and magnetic fields using the finite difference method. Then, we study the ground state binding energy of a hydrogenic impurity with a variational approach. We obtain the binding energy for QWWs consisting of the combinations of square and parabolic well potential. Our results indicate that the impurity binding energy depends strongly on the structural confinement and also, on the applied electric and magnetic field. (c) 2008 Elsevier Ltd. All rights reserved.Öğe Electron transmission in symmetric and asymmetric double-barrier structures controlled by laser fields(Academic Press Ltd- Elsevier Science Ltd, 2015) Aktas, S.; Bilekkaya, A.; Boz, F. K.; Okan, S. E.The potential profiles of symmetric and asymmetric rectangular double-barrier structures made of (Ga, Al)As/GaAs and the transmission coefficient of an electron in these systems have been investigated under intense laser field. The results show that the field alters the potential profile, and the transmission coefficient can thus be controlled. The transmission at the first resonance energy for the symmetric structure is higher than that of the asymmetric structure. Therefore, the symmetric design is feasible. The properties exhibited in this work may establish guidance to device applications. (C) 2015 Elsevier Ltd. All rights reserved.Öğe The electronic properties of a coaxial square GaAs/AlxGa1-xAs quantum well wire in an electric field(Elsevier Science Bv, 2009) Aktas, S.; Boz, F. K.; Bilekkaya, A.; Okan, S. E.The binding energy of a hydrogenic impurity in a coaxial square quantum well wire (QWW) system is investigated as a function of the barrier thickness for two different impurity positions under the electric fields. Within the effective mass approximation, the ground state energy in the presence of an external electric field applied perpendicular to the symmetry axis of the wire system is calculated using the finite difference method. Then, the ground state binding energy of a hydrogenic impurity is found employing a variational method. It is found that the binding energy in critical barrier thickness shows an increase or decrease depending on the impurity position and electric field strength. (C) 2009 Elsevier B.V. All rights reserved.Öğe Electronic transmission and dwell time on a double barrier system with an accelerating quantum well(Elsevier, 2016) Aktas, S.; Yilmaz, M.Resonant tunneling quantum structures consist of asymmetric wells and barriers have been investigated to find their optimized geometrical parameters and potential profile by the numerical calculations. The results show that the widths and the depths of the asymmetric wells have a significant effect on the transmission coefficient and the dwell time. The properties exhibited in this work may establish guidance to the device applications. (C) 2015 Elsevier B.V. All rights reserved.Öğe The energy spectrum for an electron in quantum well wires with different shapes under the electric and magnetic fields(Elsevier Science Bv, 2008) Aktas, S.; Bilekkaya, A.; Okan, S. E.The ground-state energies and wave functions for an electron in quantum well-wires (QWWs) with different shapes under the electric and magnetic fields are directly calculated using the finite difference method. It is shown that the method is able to calculate all energy states for any given QWW shape. Then, the ground-state binding energy of a hydrogenic impurity is found employing a variational method. The reliability of the results is tested against previous studies. The binding energy for QWWs consisting of the combinations of square and triangular well potential is obtained. (C) 2008 Elsevier B.V. All rights reserved.Öğe The excitons in infinite potential centered multilayered coaxial quantum wire and the magnetic field effects on their properties(Academic Press Ltd- Elsevier Science Ltd, 2020) Kes, H.; Okan, S. E.; Aktas, S.The exciton properties in a multilayered coaxial cylindrical quantum wire layered as AlAs/GaAs/ AlxGa1-xAs/GaAs/ AlxGa1-xAs are investigated. The exciton binding energies are obtained as a functions of the thicknesses of the GaAs well wires and the barrier wires formed by AlxGa1-xAs keeping the total radius of the structure constant and considering two by two variation of those. The binding energies has only one minimum for each variation and they all have approximate minimum binding energy values for their certain set of thicknesses. The magnetic field effects on the binding energies are also reported. The external magnetic field produces noticeably different effects on the electronic properties of the heavy hole and light hole excitons. The magnetic field can be shifted smaller strengths to obtain the minimum binding energy if the radius of the insulator wire in the center of the structure is increased.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 Laser field-driven potential profiles of double quantum wells(Elsevier Science Bv, 2012) Boz, F. K.; Aktas, S.; Bekar, B.; Okan, S. E.We study the potential profiles of double quantum wells with different geometries. The binding energy of an impurity under a laser field and its simultaneous application with a magnetic field is calculated by means of variational techniques. It is shown that the total potential of the structure suggests a strong control mechanism on the binding energy. (C) 2011 Elsevier B.V. All rights reserved.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 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 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.
