Mahdi Esmaeilzadeh

Accelerator Physics
PhD
31.12

Publications

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    ABSTRACT: Using non-equilibrium Green’s function, we study the spin-dependent electron transport propertiesin a zigzag silicene nanoribbon. To produce and control spin polarization, it is assumed that twoferromagnetic strips are deposited on the both edges of the silicene nanoribbon and an electric field is perpendicularly applied to the nanoribbon plane. The spin polarization is studied for both parallel and anti-parallel configurations of exchange magnetic fields induced by the ferromagnetic strips. We find that complete spin polarization can take place in the presence of perpendicular electric field for anti-parallel configuration and the nanoribbon can work as a perfect spin filter. The spin direction of transmitted electrons can be easily changed from up to down and vice versa by reversing the electric field direction. For parallel configuration, perfect spin filtering can occur even in the absence of electric field. In this case, the spin direction can be changed by changing the electron energy. Finally, we investigate the effects of nonmagnetic Anderson disorder on spin dependent conductance and find that the perfect spin filtering properties of nanoribbon are destroyed by strong disorder, but the nanoribbon retains these properties in the presence of weak disorder.
    Journal of Applied Physics 05/2015; 117(17):173913. DOI:10.1063/1.4919659 · 2.19 Impact Factor
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    ABSTRACT: We investigate the effect of an off-center donor impurity on the electronic properties of a two-dimensional quantum ring with a deformed geometrical structure in the form of an ellipse. It is shown that the dislocation of impurity from the center of elliptical quantum ring opens sizable gaps in the energy spectrum and largely deforms the eigenenergies near the ground state. As a result, the Aharonov–Bohm oscillations are quenched and the persistent electron current decreases intensely. Moreover, we show that the ground state energy exhibits a local extremum when the donor impurity is located on semi-minor (or -major) axis of the elliptic ring. The effects of the eccentricity of elliptical ring on the energy spectra and persistent current are also studied.
    Physica B Condensed Matter 02/2015; 495:36-40. DOI:10.1016/j.physb.2014.11.093 · 1.28 Impact Factor
  • Mohsen Farokhnezhad, Mahdi Esmaeilzadeh, Somayeh Ahmadi
    12th conference on condensed matter; 02/2015
  • Mohsen Farokhnezhad, Mahdi Esmaeilzadeh, Somayeh Ahmadi
    12th Conference on Condensed Matter; 02/2015
  • Golshad Kheiri, Mahdi Esmaeilzadeh
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    ABSTRACT: We study the effects of electron beam velocity spread, temperature, and self-fields on dispersion relation and growth rate in a Cherenkov radiation when an axial magnetic field is present. A generalized dispersion relation is derived and shown that in addition to cyclotron, FEL, and beam modes there are two other modes which are induced by thermal velocity of electron beam. For cyclotron mode, the effects of electron beam self-fields on the growth rate are investigated and shown that the growth rate in the presence of self-fields has a maximum value which is considerably greater than the saturation value of growth rate in the absence of self-fields. The optimum value of axial magnetic field at which the maximum growth can take place is determined for different electron beam densities. Then the effects of electron beam velocity spread and temperature on growth rate are studied and it is found that the electron beam temperature causes an increment in growth rate, while the velocity spread of electron beam has an opposite effect.
    The European Physical Journal D 02/2015; 69(1). DOI:10.1140/epjd/e2014-50626-0 · 1.40 Impact Factor
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    ABSTRACT: It is shown that, for appropriate values of electron energy, the silicene dot can work as a controllable spin polarizer. The spin polarizer can polarize the spin of transmitted electrons from nearly pure down to nearly pure up by changing the strength of an external electric field. Also, for spin polarized incoming electrons, the silicene quantum dot can invert the spin of electrons and can works as a spin inverter or a spin NOT gate. In addition, we investigate the effects of exchange field, induced by ferromagnetic substrate, on electron conductance and show that the silicene quantum dot can act as a nearly perfect spin-filter in the presence of exchange field.
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    ABSTRACT: The spin-dependent conductance and spin-polarization of a MoS2 quantum dot are studied in presence (absent) of an external electric field perpendicular to the molybdenum plane. It is shown that in absence of the electric field, the deformation of a MoS2 ribbon structure causes spin-splitting in the dot and non-prefect spin filtering is seen. Therefore, the technique could be used for designing spin-dependent devices of MoS2. Also, we show that the device could behave as a prefect spin filter and spin inverter under applying an external electric.
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    ABSTRACT: We consider a zigzag nanoribbon of MoS2 and study its spin-dependent conductance and spin-polarization in presence (absent) of an external electric field. The field is not only perpendicular to the molybdenum plane (called vertical field Ez) but also to the transport direction of electrons (called transverse field Et). It is shown that, while in the absent of the external electric field, two bands of seven bands are spin split in the valence band but no spin splitting is seen at point . Under applying the electric field we show, the ribbon behaves as a prefect spin up (down) filter if and only if the both components of the electrical field are present. Finally it is shown that, by changing the strength of , the ribbon acts as a spin inverter for fixed values of Ez .
  • Golshad Kheiri, Mahdi Esmaeilzadeh
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    ABSTRACT: We study the effects of electron beam parameters such as electron beam temperature and Lorentz relativistic factor (or electron energy) on growth rate in a realistic (three-dimensional) helical wiggler free-electron laser with ion-channel guiding. A generalized dispersion relation is derived by considering the interaction between the radiation fields and electron beam when the effects of electron beam self-fields are taken into account. The growth rate is then calculated, and it is found that, for group I orbits, there is an optimum value for electron beam density at which the growth rate goes to its maximum. Also, there is an optimum value for Lorentz relativistic factor. The effect of beam temperature is also investigated, and it is shown that the growth rate decreases considerably as beam temperature increases.
    Physica Scripta 12/2014; 89(12). DOI:10.1088/0031-8949/89/12/125603 · 1.30 Impact Factor
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    ABSTRACT: We study the spin transport and polarization properties of manganese-doped dual-guanine molecules connected to graphene leads using non-equilibrium Green's function method. It is shown that a manganese doped dual-guanine molecule is a biological semiconductor and behaves as a prefect spin filter. We show that this semiconductor can behave as a spin switch when the Rashba spin-orbit interaction is considered. In addition, it is shown that, a large conductance is observed due to the Fano-Kondo-Rashba resonance effect.
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    Hossein Mazidabadi, Hamidreza Simchi, Mahdi Esmaeilzadeh
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    ABSTRACT: Electronic and magnetic properties of graphene Möbius strips with different widths are studied using density functional theory. It is shown that the multiplicity of the Möbius strip, the cohesive energy, and the band gap energy increase with increasing the width of Möbius strip.We show that the magnetic moment of Möbius strip decreases with increasing the curvature and strain. Then the effects of an external electric field applied in the direction of the Möbius strip axis are studied and it is found that the Möbius strip keeps its metallic surface (edge) states even in the presence of the electric field. For sufficiently high applied electric field, the spin-flipping can take place in the Möbius strip. In addition, in contrast with the graphene nanoribbons, the graphene Möbius strips show half-semiconducting propertieswhen an external electric field is applied.
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    Hossein Mazidabadi, Hamidreza Simchi, Mahdi Esmaeilzadeh
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    ABSTRACT: Electronic and magnetic properties of graphene Möbius strips with different widths are studied using density functional theory. It is shown that the multiplicity of the Möbius strip, the cohesive energy, and the band gap energy increase with increasing the width of Möbius strip.We show that the magnetic moment of Möbius strip decreases with increasing the curvature and strain. Then the effects of an external electric field applied in the direction of the Möbius strip axis are studied and it is found that the Möbius strip keeps its metallic surface (edge) states even in the presence of the electric field. For sufficiently high applied electric field, the spin-flipping can take place in the Möbius strip. In addition, in contrast with the graphene nanoribbons, the graphene Möbius strips show half-semiconducting propertieswhen an external electric field is applied.
    Journal of Nanoscience and Nanotechnology 09/2014; 2(5):109-114. DOI:10.11648/j.nano.20140205.14 · 1.34 Impact Factor
  • Hamidreza Simchi, Mahdi Esmaeilzadeh, Hossein Mazidabadi
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    ABSTRACT: Spin-polarization in double-stranded DNA is studied in the presence of a magnetic field applied along its helix axis using the non-equilibrium Green's function method. The spin-polarization could be tuned by changing the magnetic field. In some special cases, the double-stranded DNA behaved as a perfect spin-filter. Furthermore, the dependency of the spin-polarization on the spin-orbit strength and dephasing strength is studied.
    Journal of Applied Physics 05/2014; 115(20):204701-204701-5. DOI:10.1063/1.4878876 · 2.19 Impact Factor
  • Leila Eslami, mahdi esmaeilzadeh
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    ABSTRACT: Spin-dependent electron transport in an open double quantum ring, when each ring is made up of four quantum dots and threaded by a magnetic flux, is studied. Two independent and tunable gate voltages are applied to induce Rashba spin-orbit effect in the quantum rings. Using non-equilibrium Green’s function formalism, we study the effects of electron-electron interaction on spin-dependent electron transport and show that although the electron-electron interaction induces an energy gap, it has no considerable effect when the bias voltage is sufficiently high. We also show that the double quantum ring can operate as a spin-filter for both spin up and spin down electrons. The spin-polarization of transmitted electrons can be tuned from �1 (pure spin-down current) to þ1 (pure spin-up current) by changing the magnetic flux and/or the gates voltage. Also, the double quantum ring can act as AND and NOR gates when the system parameters such as Rashba coefficient are properly adjusted.
    Journal of Applied Physics 02/2014; 115(8):084307. DOI:10.1063/1.4867219 · 2.19 Impact Factor
  • Hamidreza Simchi, Mahdi Esmaeilzadeh, Hossein Mazidabadi
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    ABSTRACT: The spin-dependent electron transport properties of zinc- and manganese-doped adenine molecules connected to zigzag graphene leads are studied in the zero bias regime using the non-equilibrium Green’s function method. The conductance of the adenine molecule increased and became spin-dependent when a zinc or manganese atom was doped into the molecules. The effects of a transverse electric field on the spin-polarization of the transmitted electrons were investigated and the spin-polarization was controlled by changing the transverse electric field. Under the presence of a transverse electric field, both the zinc- and manganese-doped adenine molecules acted as spin-filters. The maximum spin-polarization of the manganese-doped adenine molecule was greater than the molecule doped with zinc.
    Journal of Applied Physics 01/2014; 115(044701):1-7. DOI:10.1063/1.4863777 · 2.19 Impact Factor
  • Amiri Mَ Golsorkhtabaramiri M Esmaeilzadeh S Ghofrani F Bijani A Ghorbani L Delavar MA
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    Hamidreza Simchi, Mahdi Esmaeilzadeh, Hossein Mazidabadi
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    ABSTRACT: We study the proximity-induced superconductivity effect in a double-stranded DNA by solving the Bogoliubov-de Gennes equations and taking into account the effect of thermal fluctuations of the twist angle between neighboring base pairs. We show that the electron conductance is spin-dependent and the conductance of spin up (down) increases (decreases) due to the spin-orbit coupling. It is found that, for T<100K, the band gap energy is temperature-independent and it decreases due to the SOC. In addition, by solving the Bogoliubov-de Gennes equations and local gap parameter equation self-consistently, we find the critical temperature at which transition to superconductivity can take place.
    Journal of Applied Physics 12/2013; 115(5). DOI:10.1063/1.4864426 · 2.19 Impact Factor
  • Hamidreza Simchi, Mahdi Esmaeilzadeh, Hossein Mazidabadi
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    ABSTRACT: By omitting some carbon atoms from middle of a zigzag graphene cluster, and Hydrogen termination of sp2 orbital, we make the different porous zigzag graphene clusters, and investigate the electron transport properties of the structures by the non-equilibrium Green function method at zero bias regime. It is shown that, the conductance of porous clusters depends on the final symmetry of porous cluster and the local imbalance number (nA-nB), in which nA and nB are the number of omitted atoms from A-sublattice and B-sublattice respectively. Also it is shown that, if three carbon atoms (one type-A and two type-B sites) are omitted the conductance for |E-Ef|≥5 eV is significantly higher than the conductance of original zigzag graphene cluster due to the increment in less affected conducting channels. We show that, spin flipping occurs under Rashba spin orbit interaction at E=Ef, when three atoms are omitted from the original cluster. Therefore the local imbalance number and final symmetry of porous graphene cluster can be used as a rule for designing porous graphene devices and the device can be used in spintronic applications.
    Physica E Low-dimensional Systems and Nanostructures 12/2013; 54:220-225. DOI:10.1016/j.physe.2013.06.021 · 1.86 Impact Factor
  • Golshad Kheiri, Mahdi Esmaeilzadeh
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    ABSTRACT: A theoretical analysis is presented for dispersion relation and growth rate in a Cherenkov free electron laser with finite axial magnetic field. It is shown that the growth rate and the resonance frequency of Cherenkov free electron laser increase with increasing axial magnetic field for low axial magnetic fields, while for high axial magnetic fields, they go to a saturation value. The growth rate and resonance frequency saturation values are exactly the same as those for infinite axial magnetic field approximation. The effects of electron beam self-fields on growth rate are investigated, and it is shown that the growth rate decreases in the presence of self-fields. It is found that there is an optimum value for electron beam density and Lorentz relativistic factor at which the maximum growth rate can take place. Also, the effects of velocity spread of electron beam are studied and it is found that the growth rate decreases due to the electron velocity spread.
    Physics of Plasmas 11/2013; 20(12). DOI:10.1063/1.4841255 · 2.25 Impact Factor
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    Farhang Fallah, Mahdi Esmaeilzadeh
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    ABSTRACT: A theory is presented for exciton formation in a graphene sheet using the center-of-mass approximation. The energy levels and wavefunctions of exciton are calculated analytically which show that the exciton can form if the band gap of graphene is not zero. We show that the energy gap of graphene plays the role of the mass which if not zero, leads to formation of the excitons. It is shown that the main quantum number of the exciton ground state changes with the graphene dielectric constant. Also, all of the states are found to be four-fold degenerate. The binding energy of exciton can reach as high as 1/4 of the energy gap of graphene which is notable among the conventional quasi-2D systems. This result can play an important rule in the photonics of graphene.
    Journal of Applied Physics 08/2013; 114(7). DOI:10.1063/1.4818613 · 2.19 Impact Factor

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