461 research outputs found
Charge screening and carrier transport in AA-stacked bilayer graphene: tuning via a perpendicular electric field
The static dielectric function in AA-stacked bilayer graphene (BLG),
subjected to an electric field applied perpendicular to layers, is calculated
analytically within the random phase approximation (RPA). This result is used
to calculate the screened Coulomb interaction and the electrical conductivity.
The screened Coulomb interaction, which here can be tuned by the perpendicular
electric field, shows a power-law decay as at
long-distance limit where and are the electrical potential and the
inter-layer hopping energy respectively, indicating that the Coulomb
interaction is suppressed at high perpendicular electric fields. Furthermore,
Our results for the effect of the short-range and the long-range (Coulomb)
scattering on the electrical conductivity show that the shot-range scattering
yields a constant electrical conductivity which is not affected by the
perpendicular electric filed. While the electrical conductivity limited by the
Coulomb scattering is enhanced by the perpendicular electric field and
increases linearly in at small with a finite value at ,
indicating that we can tune the electrical conductivity in AA-stacked BLG by
applying a perpendicular electric field.Comment: 6 pages, 3 figure
Comment on "Dielectric screening and plasmons in AA-stacked bilayer graphene"
In this comment we show that some equations and results of the paper titled
"Dielectric screening and plasmons in AA-stacked bilayer graphene" are not
correct. Furthermore, we present our results which seems to be more correct.Comment: 2 pages, Comment on Phys. Rev. B 88, 115420 (2013) by R. Roldan and
L. Bre
Photo-induced spin and valley-dependent Seebeck effect in the low-buckled Dirac materials
Employing the Landauer-Buttiker formula we investigate the spin and valley
dependence of Seebeck effect in low-buckled Dirac materials (LBDMs), whose band
structure are modulated by local application of a gate voltage and off-resonant
circularly polarized light. We calculate the charge, spin and valley Seebeck
coefficients of an irradiated LBDM as functions of electronic doping, light
intensity and the amount of the electric field in the linear regime. Our
calculation reveal that all Seebeck coefficients always shows an odd features
with respect to the chemical potential. Moreover, we show that, due to the
strong spin-orbit coupling in the LBDMs, the induced thermovoltage in the
irradiated LBDMs is spin polarized, and can also become valley polarized if the
gate voltage is applied too. It is also found that the valley (spin)
polarization of the induced thermovoltage could be inverted by reversing the
circular polarization of light or reversing the direction the electric field
(only by reversing the circular polarization of light).Comment: 25 pages, 8 figures and 1 tabl
Local moment formation in bilayer graphene
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 energy is very small. But when the
impurity is adsorbed on B sublattice the magnetization is possible for limited
values of the impurity level and the on-site coulomb energy. This is due to
different local density of the low energy states at A and B sublattices which
originates from their spatial inhomogeneity. Also we show that electrical
controlling the magnetization of adatoms besides it's inhomogeneity in BLG
allow for possibility of using BLG in spintronic devices with higher potential
than graphene.Comment: 16 pages, 4 figures, Mesoscale and Nanoscale Physics
(cond-mat.mes-hall), Strongly Correlated Electrons (cond-mat.str-el
RKKY interaction in bilayer graphene
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 unusual long-distance decay of the
RKKY interaction in BLG. The intralyer RKKY interactions between two magnetic
impurities located on same sublattice, and
, decay closely as and at large
impurity distances respectively, but when they are located on opposite
sublattices the RKKY interactions exhibit decays approximately. In
the interlayer case, the RKKY interactions between two magnetic impurities
located on same sublattice show a decay close to at large impurity
distances, but if two magnetic impurities be on opposite sublattices the RKKY
interactions, and ,
decay closely as and respectively. Both intra- and
interlayer RKKY interactions have anisotropic oscillatory factors which for
intralayer case is equal to that for single layer graphene. Our results at weak
and strong interlayer coupling limits reduce to the RKKY interaction of SLG and
that of BLG in the two-bands approximation respectively.Comment: 28 pages, 7 figure
Controllable intrinsic DC spin/valley Hall conductivity in ferromagnetic silicene: Exploring a fully spin/valley polarized transport
We study intrinsic DC spin and valley Hall conductivity in doped
ferromagnetic silicene in the presence of an electric filed applied
perpendicular to silicene sheet. By calculating its energy spectrum and
wavefunction and by making use of Kubo formalism, we obtain a general relation
for the transverse Hall conductivity which can be used to obtain spin- and
valley-Hall conductivity. Our results, in the zero limit of the exchange field,
reduces to the previous results. Furthermore we discuss electrically tunable
spin and valley polarized transport in ferromagnetic silicene and obtain the
necessary conditions for observing a fully spin or valley polarized transport.Comment: 22 pages, 8 figures; to appear in Superlattices and Microstructures
journa
Electronic properties of armchair AA-stacked bilayer graphene nanoribbons
We study analytically, based on the tight-binding model, the electronic band
structure of armchair AA-stacked bilayer graphene nanoribbons (BLGNRs) in
several regimes. We apply hard-wall boundary conditions to determine the
discretion dominating on the Bloch wavefunctions in the confined direction.
First we consider an ideal case, perfect nanoribbons without any edge
deformation, and show that their electronic properties are strongly
size-dependent. We find that the narrow armchair AA-stacked BLGNRs (similar to
single-layer graphene nanoribbons) may be metallic or semiconducting depending
on their width determined by the number of dimer lines across the ribbon width,
while the wide ribbons are metallic. Then we show that, when the edge
deformation effects are taken into account, all narrow armchair AA-stacked
BLGNRs become semiconducting while the wide ribbons remain metallic. We also
investigate effects of an electric filed applied perpendicular to the
nanoribbon layers and show it can be used to tune the electronic properties of
these nanoribbons leading to a semiconducting-to-metallic phase transition at a
critical value of the electric field which depends on the nanoribbon width.
Furthermore, in all regimes, we calculate the corresponding wavefunctions which
can be used to investigate and predict various properties in these nanoribbons.Comment: 20 pages, 6 figure
Strain engineering the charged-impurity-limited carrier mobility in phosphorene
We investigate, based on the tight-binding model and in the linear
deformation regime, the strain dependence of the electronic band structure of
phosphorene, exposed to a uniaxial strain in one of its principle directions,
the normal, the armchair and the zigzag directions. We show that the electronic
band structure of strained phosphorene, for experimentally accessible carrier
densities and uniaxial strains, is well described by a strain-dependent
decoupled electron-hole Hamiltonian. Then, employing the decoupled Hamiltonian,
we consider the strain dependence of the charged-impurity-limited carrier
mobility in phosphorene, for both types of carrier, arbitrary carrier density
and in both armchair and zigzag directions. We show that a uniaxial tensile
(compressive) strain in the normal direction enhances (weakens) the anisotropy
of the carrier mobility, while a uniaxial strain in the zigzag direction acts
inversely. Moreover applying a uniaxial strain in the armchair direction is
shown to be ineffective on the anisotropy of the carrier mobility. These will
be explained based on the effect of the strain on the carrier effective mass.Comment: 31 pages, 7 figures; accepted for publication in Superlattices and
Microstructures journa
Controllable photo-induced spin and valley filtering in silicene
We study ballistic transport of Dirac electrons through a strip in silicene,
when the strip is exposed to off-resonant circularly polarized light and an
electric field applied perpendicular to the silicene plane. We show that the
conductance through the strip is spin- or/and valley-polarized. This can be
explained by spin-valley coupling in silicene, and modification of its band
structure through virtual absorption/emission processes and also by the
perpendicular electric field. The spin- (valley-) polarization can be enhanced
by tuning the light intensity and the value of the perpendicular electric
field, leading to perfect spin (valley) filtering for certain of their values.
Further, the spin (valley) polarization can be inverted by reversing the
perpendicular electric field (by reversing the perpendicular electric field or
reversing the circular polarization of the light irradiation). The conditions
necessary for the fully valley polarization is determined.Comment: 6 pages, 8 figure
Effects of doping and bias voltage on the screening in AAA-stacked trilayer graphene
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 of carrier concentrations and a
1/r^3 power law decay for the long-distance behavior of the screened coulomb
potential. We show that effects of a bias voltage can be taken into account by
a renormalization of the interlayer hopping energy to a new
bias-voltage-dependent value, indicating screening properties of biased
AAA-stacked TLG can be tuned electrically. We also find that screening
properties of doped AAA-stacked TLG, when exceeds , are
similar to that of doped SLG only depending on doping. While for
, its screening properties are a combination of SLG and
AA-stacked screening properties and they are determined by doping and the
interlayer hopping energy.Comment: 19 pages, 1 figur
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