R. Afzali

Khaje Nasir Toosi University of Technology, Teheran, Tehrān, Iran

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Publications (17)15.62 Total impact

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    ABSTRACT: In this paper, we calculate and discuss quantum teleportation and quantum entanglement with considering the interaction between neighbouring sites plus interaction existing in each sites in a quantum dots system which have been arranged one-dimensionally. With considering the spin and space entanglement in this system, we survey teleportation on it. The effect of prime neighbours interaction with respect to not considering the interaction on quantum entanglement and quantum teleportation is compared and determined.
    International Congress on Nanoscience & Nanotechnology (ICNN2014), Tarbiat Modares University, Tehran, Iran; 10/2014
  • R. Afzali, N. Ebrahimian
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    ABSTRACT: When the magnetic field is only acting on the spin of electrons, a transition from a normal to a modulated superconducting state or Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state may occur at low temperatures. A FFLO superconducting state, which accompanies an order parameter that oscillates spatially, may be stabilized by a high applied magnetic field or a molecular field. Quantum multipartite entanglement is a new procedure for investigating quantum phase transitions. In this article, we deal with the phase transition of the FFLO state of CeCoIn5 to a normal state by obtaining quantum multipartite entanglement of the system. For this purpose, using normal and anomalous Green functions and the density matrix, we obtain concurrence, as a measure of bipartite entanglement. Then, the order parameter and the magnetic -field dependence of multipartite entanglement in momentum space is calculated. The phase transition is determined, and the behavior of the system based on order parameter is discussed. Furthermore, the phase transitions of both the Bardeen-Cooper-Schrieffer (BCS) and FFLO states to the normal state are compared.
    Journal- Korean Physical Society 08/2013; 63(3):284-287. · 0.51 Impact Factor
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    ABSTRACT: We consider a mass-asymmetric polarized Fermi system in the presence of Hartree-Fock (HF) potentials. We concentrate on the BCS regime with various interaction strengths and numerically obtain the allowed values of the chemical and HF potentials, as well as the mass ratio. The functional dependence of the heat conductivity of the N-SF interface on relevant physical parameters, namely the temperature, the mass ratio, and the interaction strength, is obtained. In particular, we show that the interface conductivity starts to drop with decreasing temperature at the temperature, $T_{\text{m}}$, where the mean kinetic energy of the particles is just sufficient to overcome the SF gap. We obtain $T_{\text{m}}$ as a function of the mass ratio and the interaction strength. The variation of the heat conductivity, at fixed temperature, with the HF potentials and the imbalance chemical potential is also obtained. Finally, because the range of relevant temperatures increases for larger values of the mass ratio, we consider the $^6\text{Li}$-$^{40}\text{K}$ mixture separately by taking the temperature dependence of the pair potential into account.
    Physica C Superconductivity 05/2012; 480. · 0.72 Impact Factor
  • R. Afzali
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    ABSTRACT: Different scattering processes of quasiparticles containing a binary process, a coalescence process and a decay process in transition probabilities are taken into account. In the meantime, interaction between Bogoliubov quasiparticles as well as that between normal and superfluid components (spin up-spin down quasiparticles) of ferromagnetic superfluid 3He-A 1 are considered. Pfitzner procedure is used in the calculation of triplet and singlet quasiparticle scattering amplitude existing in transition probabilities of the collision integral of standard Boltzmann equation at melting pressure. Pfitzner procedure is extended beyond s-p approximation by adding higher angular momentum components. Then, using the results of Boltzmann equation and considering smallness of the gap close to T c↑, the change of the spin diffusion coefficients tensor of the A 1-phase of superfluid 3He close to critical temperature and melting pressure is calculated. Temperature dependence of the spin diffusion coefficient change, i.e., δD xyxy /D⌈=(3/2)(δD xzxz /D)⌉, is −0.71(1−(T/T c↑))1/2. It is also shown that interaction between normal and Bogoliubov quasiparticles (normal-superfluid components interaction) is very important to transport properties such as spin diffusion close to critical temperature. Furthermore, using s-p approximation, the prefactor of δD xyxy /D is plotted in terms of pressure; hence, the pressure dependence of δD xyxy /D is also determined.
    Journal of Statistical Physics 01/2012; 147(4). · 1.40 Impact Factor
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    ABSTRACT: Using perturbed Bogoliubov equations, we study the linear response to a weak orbital magnetic field of the heat conductivity of the normal-superfluid interface of a polarized Fermi gas at sufficiently low temperature. We consider the various scattering regions of the BCS regime and analytically obtain the transmission coefficients and the heat conductivity across the interface in an arbitrary weak orbital field. For a definite choice of the field, we consider various values of the scattering length in the BCS range and numerically obtain the allowed values of the average and species-imbalance chemical potentials. Thus, taking Andreev reflection into account, we describe how the heat conductivity is affected by the field and the species imbalance. In particular, we show that the additional heat conductivity due to the orbital field increases with the species imbalance, which is more noticeable at higher temperatures. Our results indicate how the heat conductivity may be controlled, which is relevant to sensitive magnetic field sensors/regulators at the interface.
    Physica B Condensed Matter 10/2011; 407. · 1.28 Impact Factor
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    ABSTRACT: We study the effect of a weak magnetic field on the state of the spins of a pair of electrons forming a Cooper pair in an s-wave superconductor. By perturbatively solving time-dependent Bogoliubov equations up to first order, we obtain the two-particle Green function, and whence the two-electron spin-space density matrix. It appears that up to first order approximation, the spin state of a Cooper pair retains the form of a Werner state. This state is then examined in the sense of quantum correlations, i.e., quantum discord. Comment: 4 pages, 1 figure
    11/2010;
  • R. Afzali, F. Rahmati
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    ABSTRACT: The second viscosity coefficients of A1-phase of superfluid 3He are calculated at low temperatures and melting pressure by using the standard Boltzmann equation approach. The Pfitzner procedure has been used for the quasiparticle scattering amplitude which appears in collision integrals of Boltzmann equation. Temperature dependence of components of second viscosity coefficients, (ζ1)xx(=(ζ1)yy), (ζ1)zz and (ζ2)xx(=(ζ2)yy=(ζ2)zz) are proportional to ((s2)↑)2T6, ((s2)↑)2T4 and ((s2)↓)2T2, respectively, where the spin-dependent (s2)↓ is found to be constant with respect to temperature, while (s2)↑ has a 1/T2 dependence. Therefore, (ζ1)xx and (ζ2)xx are proportional to T2, and (ζ1)zz and the other viscosity coefficient ζ3 are constant.
    Physica B Condensed Matter 01/2010; 405(4):1050-1054. · 1.28 Impact Factor
  • R. Afzali, F. Pashaee
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    ABSTRACT: The spin diffusion coefficient tensor of the A1-phase of superfluid 3He at low temperatures and melting pressure is calculated using the Boltzmann equation approach and Pfitzner procedure. Then considering Bogoliubov-normal interaction, we show that the total spin diffusion is proportional to 1/T2, the spin diffusion coefficient of superfluid component D\uparrowxzxz is proportional to T-2, and the spin diffusion coefficient of super-fluid component D\uparrowxxxx (=D\uarrowxyxy) is independent of temperature. Furthermore, it is seen that superfluid components play an important role in spin diffusion of the A1-phase.
    Modern Physics Letters B 01/2009; 23(12):1603-1610. · 0.48 Impact Factor
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    Reza Afzali
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    ABSTRACT: The penetration depth of FFLO d-wave superconductors is calculated, in presence of additional magnetic field for both parallel and perpendicular to the internal FFLO magnetic field, when the nonlocal effects are dominated. The generalized Gorkov equations have been used to obtain the linearized response kernel. It is shown that extra term added to total kernel with no spatially gap is proportional to the momentum of FFLO Cooper pairs, Q. For the case parallel to the internal FFLO magnetic field, below a crossover temperature T*, it is shown that Lambda(T)-Lambda(0) is proportional to T^3 for both specular reflecting and diffusive boundary. It is noted that both terms in penetration depth with and without Q dependence have the same temperature dependence but magnetic field dependence are different(the terms without and with Q dependence are proportional to 1/h' and 1/(h'^2) respectively). Also nonlocal effect on penetration depth of FFLO state in reign T>>T* obtains temperature dependence T^4. Furthermore, when external magnetic test-field is perpendicular to internal FFLO magnetic field, it is shown that nonlocal effects on penetration depth give the same Q and temperature dependence as the parallel case but with different internal and additional magnetic field dependences.
    05/2008;
  • R. Afzali
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    ABSTRACT: Quantum fluctuation and tunneling of a superconducting nano-grain placed in magnetic field are analytically considered in frequency space. Tunneling fluctuation of a superconducting grain to superposition of superconducting and paramagnetic states are investigated. By using Fourier transformation, instanton equations are solved. Then, by supposing smallness of deviation of order parameter with respect to BCS energy gap, matrix Green function of system and self-consistent equation of order parameter in frequency space, at first approximation, for both d -wave and s -wave case, is obtained. Based on analytic form of order parameter of system at Fermi sphere, quantum phase transition of a s-wave superconducting grain is shown. For d-wave case, investigating of tunneling process at first approximation is subtle and needs further attention. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 07/2006; 3(9):3130 - 3134.
  • R. Afzali, N. Ebrahimian
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    ABSTRACT: The diffusive thermal conductivity tensor of the A 1-phase of superfluid 3He at low temperatures and melting pressure are calculated by s-p approximation, by using the Boltzmann equation approach. We obtain that the elements of the diffusive thermal conductivities, Kxx, Kyy, and Kzz, are proportional to T -1. Then we compare the results of this paper and our results of thermal conductivity based on Pfitzner procedure. Temperature dependence of both results is equal but numerical coefficients of them are little different. Also we show that Boguliubov-normal interaction is important in comparison to other interactions.
    physica status solidi (c) 01/2006; 3(9):3321-3324.
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    R. Afzali, A. Rezakhani T
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    ABSTRACT: A nano-scale s-wave superconducting grain, coupled to a normal metallic contact through a tunnelling junction, is placed in an external magnetic field. We suppose that effect of this quantum tunnelling on the Fourier transform of the order parameter is in the form of a small additive correction to the BCS order parameter. At the first order approximation in terms of this correction term and by using an instanton method, the related Green functions (in frequency space) are obtained. By establishing a self-consistent configuration an analytic formula for the order parameter is also found. We also show that a departure from superconductivity can be captured by this formula. This change of state is indeed a manifestation of a quantum transition induced by quantum fluctuations. In this sense, this is an advantage of our simple method which, like other more elaborate methods, can detect a quantum transition in the state of the grain.
    Chinese Physics Letters 01/2006; 23(4):967-970. · 0.92 Impact Factor
  • R Afzali, N Ebrahimian
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    ABSTRACT: The diffusive thermal conductivity tensor of the A1-phase of superfluid 3He at low temperatures and melting pressure are calculated beyond the s–p approximation, by using the Boltzmann equation approach. The interaction between normal–normal, normal–Bogoliubov and Bogoliubov–Bogoliubov quasiparticles in the collision integrals are considered for important scattering processes such as binary process. At low temperatures, we show that the scattering between Bogoliubov and normal quasiparticles in binary processes plays an important role in the A1-phase, and Bogoliubov–Bogoliubov interaction is ignorable. We show that the two normal and superfluid components take part in elements of the diffusive thermal conductivity tensor differently. We obtain the result that the elements of the diffusive thermal conductivities, Kxx, Kyy and Kzz, are proportional to T−1, and also that the superfluid components of the diffusive thermal conductivity tensor, and , are proportional to T3 and T, respectively.
    Journal of Physics Condensed Matter 06/2005; 17(28):4441. · 2.22 Impact Factor
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    M. A. Shahzamanian, R. Afzali
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    ABSTRACT: Quasiparticle relaxation rate, τp−1, and the shear viscosity tensor of the A1-phase of superfluid 3He are calculated at low temperatures and melting pressure, by using Boltzmann equation approach in momentum space. The collision integral is written in terms of inscattering and outscattering collision integrals. The interaction between normal and Bogoliubov quasiparticles is considered in calculating transition probabilities in the binary, decay and coalescence processes. We obtain that both τp↑−1 and τp↓−1 are proportional to T2. The shear viscosities ηxy, ηxz and ηzz are proportional to (T/Tc)−2. The constant of proportionality of the shear viscosity tensor is in nearly good agreement with the experimental results of Roobol et al., and our exact theoretical calculation.
    Physica B Condensed Matter 01/2004; 348(1):108-114. · 1.28 Impact Factor
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    M. A. Shahzamanian, R. Afzali
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    ABSTRACT: The shear viscosity tensor of the A1-phase of superfluid 3He is calculated at low temperatures and melting pressure, by using the Boltzmann equation approach. The two normal and superfluid components take part in elements of the shear viscosity tensor differently. The interaction between normal and Bogoliubov quasiparticles in the collision integrals is considered in the binary, decay, and coalescence processes. We show that the elements of the shear viscosities ηxy, ηxz, and ηzz are proportional to (T/Tc)−2. The constant of proportionality is in nearly good agreement with the experimental results of Roobol et al.
    Annals of Physics 01/2004; 309(2):281-294. · 3.32 Impact Factor
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    M A Shahzamanian, R Afzali
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    ABSTRACT: The scattering processes between the quasiparticles in the spin-up superfluid and the quasiparticles in the spin-down normal fluid are added to the other relevant scattering processes in the Boltzmann collision terms. The Boltzmann equation has been solved exactly for temperatures just below Tc1. The shear viscosity component of the A1-phase drops as C1 (1 − T /Tc1)1/2. The numerical factor C1 is in fairly good agreement with the experiments.
    Journal of Physics Condensed Matter 01/2003; 15(3):367. · 2.22 Impact Factor