### Browsing by Author "Tanatar, Bilal"

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Item Open Access Analysis of the phase lapse problem in closed interferometers(Elsevier B.V., 2012) Tolea, M.; Moldoveanu, V.; Dinu, I. V.; Tanatar, BilalShow more We investigate the connection between the asymmetry of the Fano resonances in a mesoscopic interferometer with an embedded quantum dot and the π lapses in the phase of the bare dot transmittance. Consecutive Fano resonances with the same (opposite) sign of the Fano parameter imply the presence (absence) of a phase lapse with π between the corresponding resonances of the dot. Our results suggest that the famous phase lapse problem, first reported by Schuster et al. [R. Schuster, E. Buks, M. Heiblum, D. Mahalu, V. Umansky, H. Shtrikman, Nature 385 (1997) 417], can therefore be experimentally addressed in closed interferometers. It is also proposed that the Fano effect can be used to extract the phase distributions of the eigenfunctions for a mesoscopic 2D shape, via the parity of the resonances. In the presence of electron-electron interaction, one can calculate the phases of the T-matrix elements. The numerical results lead to the same conclusions as for the non-interacting case.Show more Item Open Access Analytical expressions for the local-field corrections in double-layer electron systems(Academic Press, 1999) Tanatar, BilalShow more We develop an extension of the sum-rule version of the Singwi, Tosi, Land, and Sjolander (STLS) scheme applied to a double-layer electron system. We present analytical expressions for the intralayer and interlayer static structure factors and corresponding local-field corrections which agree quite well with the full STLS calculations. Some applications of our basic results and further generalizations of our method are discussed.Show more Item Open Access Angular dependence of upper critical field in two-band Ginzburg-Landau theory(Elsevier B.V., 2007) Askerzade, I. N.; Tanatar, BilalShow more Generalization of two-band Ginzburg-Landau (GL) theory to the case of anisotropic mass is presented. The temperature dependence of the anisotropy parameter of upper critical field γc 2 (T) = Hc 2∥ (T) / Hc 2⊥ (T) and angular dependence of Hc2(θ, T) are calculated using anisotropic mass two-band Ginzburg-Landau theory of superconductors. It is shown that, with decreasing temperature anisotropy parameter γc2(T) is increased. Results of our calculations are in agreement with experimental data for single crystal MgB2. © 2007.Show more Item Open Access Anisotropy of critical fields in MgB2: Two-Band ginzburg-landau theory for layered superconductors(IOP Institute of Physics Publishing, 2009) Askerzade, I. N.; Tanatar, BilalShow more The temperature dependence of the anisotropy parameter of upper critical field γHc2 (T) Hc2 (T)/Hc2 (T) and London penetration depth γλ(T) λ(T)/λ (T) are calculated using two-band Ginzburg-Landau theory for layered superconductors. It is shown that, with decreasing temperature the anisotropy parameter γHc2 (T) is increased, while the London penetration depth anisotropy γλ(T) reveals an opposite behavior. Results of our calculations are in agreement with experimental data for single crystal MgB2 and with other calculations. Results of an analysis of magnetic field Hc1 in a single vortex between superconducting layers are also presented.Show more Item Open Access Band-gap renormalization in quantum wire systems: dynamical correlations and multi-subband effects(Institute of Physics Publishing, 2000) Güven, K.; Tanatar, Bilal; Bennett, C. R.Show more We study the band-gap renormalization m a model semiconductor quantum wire due to the exchange-correlation effects among the charge carriers. We construct a two-subband model for the quantum wire, and employ the GW-approximation to obtain the renormalized quasi-particle energies at the optical band edge. The renormalization is calculated as a function of electron-hole plasma density and the wire radius. Our results show that the very presence of the second subband affects the renormalization process even in the absence of occupation by the carriers. We compare the fully dynamical random-phase approximation results to the quasi-static case in order to emphasize the dynamical correlation effects. Effects of electron-phonon interaction within the two-subband model are also considered.Show more Item Open Access Band-gap renormalization in quantum wires(TÜBİTAK, 1999) Güven, Kaan; Bennett, C.R.; Tanatar, BilalShow more Improved techniques in semiconductor fabrication increased the interest in quantum wire structures, because of their opto-electronic device application possibilities. Many-body interactions among the electrons and holes in the wire lead to the band-gap renormalization (BGR), which in turn affect the optical properties of the system. We study the BGR within the random-phase approximation incorporating the dynamical effects, and investigate the density dependence.Show more Item Open Access Band-gap renormalization in quasi-one-dimensional electron-hole systems(Institute of Physics Publishing Ltd, 1996) Tanatar, BilalShow more We study the band-gap renormalization (BGR) in semiconductor quantum wires. Assuming an electron-hole system in quasi-equilibrium, we employ the random-phase approximation (RPA) and beyond (e.g., local-field corrections) to calculate the electron and the hole self-energies. The plasmon-pole approximation to the static dielectric function ε(q) agrees well with the RPA result. Our results for the BGR are compared with the recent experimental measurements and other theoretical calculations.Show more Item Open Access Band-gap renormalization in quasi-one-dimensional systems(Kluwer Academic Publishers, 1997) Tanatar, Bilal; Abstreiter, G.; Aydınlı, Atilla; Leburton, J. -P.Show more Item Open Access Bistable behavior of a two-mode Bose-Einstein condensate in an optical cavity(IOP Institute of Physics Publishing, 2013-01-11) Safaei, S.; Mustecaplioglu, Ö. E.; Tanatar, BilalShow more We consider a two-component Bose-Einstein condensate in a one-dimensional optical cavity. Specifically, the condensate atoms are taken to be in two degenerate modes due to their internal hyperfine spin degrees of freedom and they are coupled to the cavity field and an external transverse laser field in a Raman scheme. A parallel laser also excites the cavity mode. When the pump laser is far detuned from its resonance atomic transition frequency, an effective nonlinear optical model of the cavity-condensate system is developed under the discrete mode approximation (DMA), while matter-field coupling has been considered beyond the rotating wave approximation. By analytical and numerical solutions of the nonlinear dynamical equations, we examine the mean cavity field and population difference (magnetization) of the condensate modes. The stationary solutions of both the mean cavity field and normalized magnetization demonstrate bistable behavior under certain conditions for the laser pump intensity and matter-field coupling strength.Show more Item Open Access Bose-Einstein condensation in a one-dimensional interacting system due to power-law trapping potentials(American Physical Society, 1999) Bayındır, Mehmet; Tanatar, Bilal; Gedik, Z.Show more We examine the possibility of Bose-Einstein condensation in one-dimensional interacting Bose gas subjected to confining potentials of the form V ext(x) = V 0(|x|/a) γ, in which γ<2, by solving the Gross-Pitaevskii equation within the semiclassical two-fluid model. The condensate fraction, chemical potential, ground state energy, and specific heat of the system are calculated for various values of interaction strengths. Our results show that a significant fraction of the particles is in the lowest energy state for a finite number of particles at low temperature, indicating a phase transition for weakly interacting systems.Show more Item Open Access Bose-Einstein condensation in a two-dimensional, trapped, interacting gas(American Physical Society, 1998) Bayındır, Mehmet; Tanatar, BilalShow more We study the Bose-Einstein condensation phenomenon in a two-dimensional (2D) system of bosons subjected to a harmonic-oscillator-type confining potential. The interaction among the 2D bosons is described by a δ function in configuration space. Solving the Gross-Pitaevskii equation within the two-fluid model we calculate the condensate fraction, ground-state energy, and specific heat of the system. Our results indicate that interacting bosons have similar behavior to those of an ideal system for weak interactions.Show more Item Open Access Bose-Einstein condensation of noninteracting charged Bose gas in the presence of external potentials(Elsevier Science Publishers B.V., 2001) Bayındır, Mehmet; Tanatar, BilalShow more We investigate thermodynamic properties of noninteracting charged bosons in the presence of externally applied electric and magnetic fields. Using the semiclassical density of states, we obtain the condensate fraction, chemical potential, total energy, and specific heat of a system of finite number of charged Bose particles. We conclude that Bose-Einstein condensation of the charged Bose gas occurs in the crossed electric and magnetic fields.Show more Item Open Access Characteristic temperatures of a triplon system of dimerized quantum magnets(World Scientific Publishing Co. Pte. Ltd., 2021) Rakhimov, Abdulla; Nishonov, M.; Rani, Luxmi; Tanatar, BilalShow more Exploiting the analogy between ultracold atomic gases and the system of triplons, we study magneto-thermodynamic properties of dimerized quantum magnets in the framework of Bose–Einstein condensation (BEC). Particularly, introducing the inversion (or Joule–Thomson) temperature TJT as the point where Joule–Thomson coefficient of an isenthalpic process changes its sign, we show that for a simple paramagnet, this temperature is infinite, while for three-dimensional (3D) dimerized quantum magnets it is finite and always larger than the critical temperature Tc of BEC. Below the inversion temperature TShow more Item Open Access Charged bosons in a quasi-one-dimensional system(American Physical Society, 2000) Tanatar, Bilal; Davoudi, B.; Kohandel, M.Show more The ground-state properties of a system of charged bosons in a quasi-one-dimensional model with a neutralizing background are investigated within the hypernetted-chain approximation. Strong correlation effects drive the system from a homogeneous fluid phase toward a more ordered structure akin to Wigner crystallization in higher-dimensional charged quantum systems. The ordered phase of charged bosons is signaled by the development of a peak in the static structure factor, which is analyzed as a function of the density and the lateral width of the one-dimensional structure. We also calculate the pair-distribution function, the ground-state energy, and the local-field correction, and compare our results with other theoretical approaches.Show more Item Open Access Coherent and incoherent transport through T-shaped double quantum dots(Elsevier B.V., 2008) Moldoveanu, V.; Ţolea, M.; Tanatar, BilalShow more We investigate the measurement induced dephasing of the Fano effect in the electronic transport through a double quantum dot mesoscopic interferometer coupled to a charge detector. The current and the differential conductance are computed within the Keldysh formalism, taking into account of the inelastic processes due to the dot-detector interaction. We show that the visibility of the Fano lineshape is reduced by applying a finite bias on the charge detector.Show more Item Open Access Collective excitations and instabilities in double-wire electron-hole systems(Institute of Physics Publishing Ltd., 1997) Mutluay, N.; Tanatar, BilalShow more We investigate the collective excitations in a double-wire system of spatially separated electrons and holes. Self-consistent local-field factors are used to describe the exchange-correlation effects at low densities. Plasmon dispersions and the dynamic structure factor S(q, w) are studied. Charge-density-wave instabilities in these structures are examined within the linear response theory at small and finite q-values.Show more Item Open Access Collective excitations and screened interactions in two-dimensional charged Bose systems(Institute of Physics Publishing Ltd., 1995) Tanatar, Bilal; Das, A. K.Show more We study the collective excitation spectrum of a two-dimensional charged Bose gas interacting via long- and short-range potentials. The resulting plasmon dispersions depend on the type of interaction. Extending our results to a double-layer system, we calculate the dispersion relations of ensuing optical and acoustic plasmons, and screened interactions. The effective interactions exhibit attractive parts which may have interesting consequences. Comparison of our results with a two-dimensional electron gas is made.Show more Item Open Access Collective excitations in quasi-one-dimensional electron systems under a magnetic field(American Physical Society, 1993) Tanatar, Bilal; Constantinou, N. C.Show more A study of the magnetoplasmons of a cylindrical quasi-one-dimensional electron system is given in the presence of an axial magnetic field B. A two-subband system is considered and the dispersion relations for both intrasubband and intersubband magnetoplasmons are obtained using the exact infinite wall eigenfunctions. It is demonstrated that the application of a longitudinal B changes the mode frequencies for both types of excitations. The model includes both local-field corrections, which are shown to be important, and the Hartree potential, which is given in closed form. © 1993 The American Physical Society.Show more Item Open Access Collective excitations of strongly coupled bilayer charged Bose liquids in the third-frequency-moment sum rule(The American Physical Society, 2008) Tas, M.; Tanatar, BilalShow more We calculate the collective excitation modes of strongly coupled bilayer charged Bose systems. We employ the dielectric matrix formulation to study the correlation effects within the random-phase approximation (RPA), the self consistent field approximation Singwi, Tosi, Land, and Sjölander (STLS), and the quasilocalized charge approximation (QLCA), which satisfies the third-frequency-moment (〈ω3〉) sum rule. We find that the QLCA predicts a long-wavelength correlation-induced energy gap in the out-of-phase plasmon mode, similar to the situation in electronic bilayer systems. The energy gap and the plasmon density of states are studied as a function of interlayer separation and coupling parameter rs. The results should be helpful for experimental investigations.Show more Item Open Access Collective modes in a bilayer dipolar fermi gas and the dissipationless drag effect(Springer, 2013) Tanatar, BilalShow more We consider the collective modes of a bilayer dipolar Fermi system in which the particles interact via long range (∼1/r 3) interaction. Assuming that each layer has a background flow which varies little and that the dynamics of the superfluid near T=0 is the same as that of a normal fluid, we obtain the dispersion relations for the collective modes in the presence of background flow. Decomposing the background flow into two parts, the center-of-mass flow and counterflow, we focus on the properties of the counterflow. We first find an estimate of the change in the zero-point energy ΔE ZP due to counterflow for a unit area of bilayer. Combining this with the free energy F of the system and taking the partial derivatives with respect to background velocities in the layers, we determine the current densities which reveal the fact that current in one layer does not only depend on the velocity in the same layer but also on the velocity of the other layer. This is the drag effect and we calculate the drag coefficient.Show more