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Sep 21, 2013
09/13
by
Rostam Moradian
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We added an extra condition, original lattice symmetry of chosen cluster around cluster central site, to the cluster approximation methods with periodic boundary condition such as dynamical cluster approximation (DCA), effective medium approximation (EMSCA) and nonlocal coherent potential approximation (NLCPA). For each cluster size, this condition leads to a unique cluster wave vectors set in the first Brillouin zone (FBZ) where they preserve full symmetry of first Brillouin zone around ${\bf...
Source: http://arxiv.org/abs/0905.0766v3
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Sep 20, 2013
09/13
by
Rostam Moradian
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Effective medium super-cell approximation method which is introduced for disordered systems is extended to a general case of interacting disordered systems. We found that the dynamical cluster approximation (DCA) and also the non local coherent potential approximation (NLCPA) are two simple case of this technique. Whole equations of this formalism derived by using the effective medium theory in real space.
Source: http://arxiv.org/abs/cond-mat/0405357v2
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Sep 20, 2013
09/13
by
Rostam Moradian
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We introduce a new real space super cell approximation method for treating the electronic states of disordered systems. This method is general and allows both randomness in the on-site energies and in the hopping integrals. In the special case of randomness in the on-site energies only, this method is equivalent to the Non Local Coherent Potential Approximation (NLCPA) derived previously.
Source: http://arxiv.org/abs/cond-mat/0405356v1
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Sep 20, 2013
09/13
by
Rostam Moradian
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We investigate a disordered single-walled carbon nanotube (SWCNT) in an effective medium super cell approximation (EMSCA). First type of disorder that we consider is the presence of vacancies. Our results show that the vacancies induce some bound states on their neighbor host sites, leading to the creation of a band around the Fermi energy in the SWCNT average density of states.Second type of disorder considered is a substitutional $B_{cb}N_{cn}C_{1-cb-cn}$ alloy due to it's applications in...
Source: http://arxiv.org/abs/cond-mat/0405364v1
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Sep 18, 2013
09/13
by
Rostam Moradian; Hamzeh Mousavi
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We investigate validity of Anderson's theorem (AT) for disordered s-wave superconductors in a negative U Hubbard model with random on-site energies, $\epsilon_{i}$. The superconducting critical temperature, $T_{c}$, is calculated in the coherent potential approximation (CPA) as a function of impurity concentration, $c$, the random potentials for different band filling. In contradiction to Anderson's theorem, we found that $T_{c}$ is dramatically sensitive with respect to $c$ and $\epsilon_{i}$....
Source: http://arxiv.org/abs/cond-mat/0505092v1
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3.0
Jun 30, 2018
06/18
by
Yawar Mohammadi; Rostam Moradian
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We study magnetism of an adatom adsorbed on AA-stacked bilayer graphene (BLG) in both unbiased and biased cases, using the Anderson impurity model. We find different magnetic phase diagrams for the adatom, depending on the energy level of the adatom, which varies from the magnetic phase diagram of adatom in normal metals to that in graphene. This is due to the individual energy dependence of the density of states (DOS) of AA-stacked BLG and anomalous broadening of the adatom energy level....
Topics: Mesoscale and Nanoscale Physics, Strongly Correlated Electrons, Condensed Matter
Source: http://arxiv.org/abs/1406.7388
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10.0
Jun 30, 2018
06/18
by
Yawar Mohammadi; Rostam Moradian
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The local properties of bilayer graphene (BLG) due to the spatial inhomogeneity of its sublattices are of interest. We apply Anderson impurity model to consider the local moment formation on a magnetic impurity which could be adsorbed on different sublattices of BLG. We find different features for the impurity magnetization when it is adsorbed A and B sublattices. The impurity adsorbed on A sublattice can magnetize even when the impurity level is above the Fermi level and the on-site coulomb...
Topics: Mesoscale and Nanoscale Physics, Strongly Correlated Electrons, Condensed Matter
Source: http://arxiv.org/abs/1406.7384
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3.0
Jun 30, 2018
06/18
by
Yawar Mohammadi; Rostam Moradian
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We study the RKKY interaction between two magnetic impurities located on same layer (intralayer case) or on different layers (interlayer case) in undoped bilayer graphene in the four-bands model, by directly calculating the Green functions in the eigenvalues and eigenvectors representation. Our results show that both intra- and interlayer RKKY interactions between two magnetic impurities located on same (opposite) sublattice are always ferromagnetic (antiferromagnetic). Furthermore we find...
Topics: Mesoscale and Nanoscale Physics, Strongly Correlated Electrons, Condensed Matter
Source: http://arxiv.org/abs/1407.7959
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64
Sep 19, 2013
09/13
by
{Rostam Moradian; Ali Fathalian
texts
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Possibility of a ferromagnetic semiconductor single wall carbon nanotube (SWCNT), where ferromagnetism is due to coupling between doped magnetic impurity on a zigzag SWCNT and electrons spin, is investigate. We found, in the weak impurity-spin couplings, at low impurity concentrations the spin up electrons density of states remain semiconductor while the spin down electrons density of states shows a metallic behavior. By increasing impurity concentrations the semiconducting gap of spin up...
Source: http://arxiv.org/abs/cond-mat/0507503v1
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3.0
Jun 30, 2018
06/18
by
Yawar Mohammadi; Rostam Moradian; Farzad Shirzadi Tabar
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We calculate the static polarization of AAA-stacked trilayer graphene (TLG) and study its screening properties within the random phase approximation (RPA) in all undoped, doped and biased regimes. We find that the static polarization of undoped AAA-stacked TLG is a combination of the doped and undoped single layer graphene static polarization. This leads to an enhancement of the dielectric background constant along a Thomas-Fermi screening with the Thomas-Fermi wave vector which is independent...
Topics: Mesoscale and Nanoscale Physics, Condensed Matter
Source: http://arxiv.org/abs/1406.7385
