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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 Coulomb crystallites from harmonically confined charged bosons in two dimensions(Iop Publishing Ltd, 2008) Mese, A. I.; Capuzzi, P.; Akdeniz, Z.; Okan, S. E.; Tosi, M. P.We exploit rotational-symmetry breaking in the one-body density to examine the formation of structures in systems of N strongly coupled charged bosons with logarithmic repulsions inside isotropic two-dimensional harmonic traps, with N in the range from 2 to 7. The results serve as a map for ordered arrangements of vortices in a trapped Bose-Einstein condensate. Two types of N-body wavefunctions are assumed: (i) a permanent vertical bar psi(WM)> of N identical Gaussian orbitals centred at variationally determined sites, and (ii) a permanent vertical bar psi(SM)> of N orthogonal orbitals built from harmonic-oscillator energy eigenstates. With increasing coupling strength, the bosons in the vertical bar psi(WM)> orbitals localize into polygonal-ringlike crystalline patterns ('Wigner molecules'), whereas the wavefunctions vertical bar psi(SM)> describe low energy excited states containing delocalized bosons as in supersolid crystallites ('supermolecules'). For N = 2 at strong coupling both states describe a Wigner dimer.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 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 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 The multilayered spherical quantum dot under a magnetic field(Elsevier Science Bv, 2010) Boz, F. K.; AktasA, S.; Bilekkaya, A.; Okan, S. E.The binding energy of an impurity located at the center of multilayered spherical quantum dot (MSQD) is reported as a function of the dot and barrier thickness for different alloy compositions under the influence of a magnetic field. Within the effective mass approximation, the binding energy has been calculated using the fourth order Runge-Kutta method without magnetic field. A variational approach has been employed if a magnetic field is present. The binding energy in MSQD with equal dot and barrier thickness is calculated. It is shown that the binding energy in MSQD differs from that of a single quantum dot. Also, the geometry is dominant on the binding energy for thin MSQDs, but the magnetic field becomes more effective for thick MSQDs. (C) 2010 Elsevier B.V. All rights reserved.Öğe The role of confinement and shape on the binding energy of an electron in a quantum dot(Elsevier Science Bv, 2008) Sucu, S.; Mese, A. I.; Okan, S. E.The impurity ground state binding energy in cubic and cylindrical GaAs/AlAs quantum dots has been calculated using a variational procedure within the effective mass approximation. We exploit the impurity ground state energy under an external electric field strongly affected by the anisotropy of the quantum dots more than their shapes. (C) 2008 Elsevier B.V. All rights reserved.Öğe Spatial electric and. axial magnetic fields effect in GaAs-AlAs quantum wires(Elsevier, 2007) Akankan, O.; Okan, S. E.; Akbas, H.In this work. we investigated the effect of both spatial electric and axial magnetic fields on the impurity ground state energy and the polarization of a donor impurity in square GaAs/AlAs QWWs. We show that the impurity ground state energy and the polarization depends strongly not only on the width of QWW, but also on the applied spatial component of the electric field and the impurity position. (c) 2006 Elsevier B.V. All rights reserved.
