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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 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 of dielectric constant on binding energy and impurity self-polarization in a GaAs-Ga1-xAlxAs spherical quantum dot(Indian Assoc Cultivation Science, 2017) Mese, A. I.; Cicek, E.; Erdogan, I.; Akankan, O.; Akbas, H.The ground state, 1s, and the excited state, 2p, energies of a hydrogenic impurity in a GaAs-Ga1-xAlxAs spherical quantum dot, are computed as a function of the donor positions. We study how the impurity self-polarization depends on the location of the impurity and the dielectric constant. The excited state anomalous impurity self-polarization in the quantum dot is found to be present in the absence of any external influence and strongly depends on the impurity position and the radius of the dot. Therefore, the excited state anomalous impurity self-polarization can give information about the impurity position in the system. Also, the variation of E-b1s and E-b2p with the dielectric constant can be utilized as a tool for finding out the correct dielectric constant of the dot material by measuring the 1s or 2p state binding energy for a fixed dot radius and a fixed impurity position.Öğe The effects of geometrical shape and impurity position on the self-polarization of a donor impurity in an infinite GaAs/AlAs tetragonal quantum dot(Indian Assoc Cultivation Science, 2021) Akankan, O.; Erdogan, I.; Mese, A. I.; Cicek, E.; Akbas, H.Using the variational method within the effective-mass approximation, the effects of geometrical shape and impurity position on the ground-state self-polarization and binding energy of a donor impurity are theoretically studied for the infinite GaAs/AlAs tetragonal quantum dot. We have found that the ground-state self-polarization and binding energy depend on geometrical shape and impurity-AlAs layer distance.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 effect on the normalized self-polarization, self-polarization and binding energy in square quantum wells made of different materials(Elsevier, 2023) Mese, A. I.; Cicek, E.; Ozkapi, S. G.; Ozkapi, B.; Erdogan, I.In this study, we examine the effect of the laser field on normalized self-polarization, self-polarization, and binding energy in square quantum wells made of four different materials under effective mass approximation. The effects of well width, laser field, and impurity position on normalized self-polarization, self-polarization, and binding energies are shown in detail. The subband energies are obtained by the finite difference method, and the impurity energies are calculated by the variational method. The laser field significantly affects binding energy, self-polarization, and normalized self-polarization. The term normalized self-polarization is defined for the first time in this study. This allows a more detailed examination of the self-polarization change depending on the impurity position. Examining the laser field effect, especially in square quantum wells made of different materials, will provide researchers with helpful information about the importance of material selection in calculating binding energy, self-polarization, and normalized self-polarization.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 The size effect of the tetragonal quantum dot on the self-polarization under the spatial electric field(Indian Assoc Cultivation Science, 2024) Cicek, E.; Mese, A. I.; Akankan, O.; Akbas, H.In this paper, the effect of the spatial electric field on the hydrogenic impurity self-polarization and binding energy in a GaAs/AlAs tetragonal quantum dot are calculated by the variational method based on the effective mass approximation. We have shown that the self-polarization and binding energy of a hydrogenic impurity in a tetragonal quantum dot depends strongly on the theta angle of the spatial electric field, the size effect (L-z/L ratio (M)), the volume of the dot, and impurity position. Furthermore, we define the angle theta(max), which aligns the spatial electric field vector with the position vector of the hydrogenic impurity on the diagonal axis. It has been noted that self-polarization reaches its peak at this particular angle.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 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.
