12,155 research outputs found
On the Solution of Topological Landau-Ginzburg Models with
The solution is given for the topological matter model whose underlying
conformal theory has Landau-Ginzburg model W=-\qa (x^4 +y^4)+\af x^2y^2.
While consistency conditions are used to solve it, this model is probably at
the limit of such techniques. By using the flatness of the metric of the space
of coupling constants I rederive the differential equation that relates the
parameter \af\ to the flat coordinate . This simpler method is also applied
to the -model.Comment: 7p
Energy gap tuning in graphene on hexagonal boron nitride bilayer system
We use a tight binding approach and density functional theory calculations to
study the band structure of graphene/hexagonal boron nitride bilayer system in
the most stable configuration. We show that an electric field applied in the
direction perpendicular to the layers significantly modifies the electronic
structure of the whole system, including shifts, anticrossing and other
deformations of bands, which can allow to control the value of the energy gap.
It is shown that band structure of biased system may be tailored for specific
requirements of nanoelectronics applications. The carriers' mobilities are
expected to be higher than in the bilayer graphene devices.Comment: 10 pages, 7 figures, submitted to Physical Review
Transport in the XX chain at zero temperature: Emergence of flat magnetization profiles
We study the connection between magnetization transport and magnetization
profiles in zero-temperature XX chains. The time evolution of the transverse
magnetization, m(x,t), is calculated using an inhomogeneous initial state that
is the ground state at fixed magnetization but with m reversed from -m_0 for
x0. In the long-time limit, the magnetization evolves into a
scaling form m(x,t)=P(x/t) and the profile develops a flat part (m=P=0) in the
|x/t|1/2 while it
expands with the maximum velocity, c_0=1, for m_0->0. The states emerging in
the scaling limit are compared to those of a homogeneous system where the same
magnetization current is driven by a bulk field, and we find that the
expectation values of various quantities (energy, occupation number in the
fermionic representation) agree in the two systems.Comment: RevTex, 8 pages, 3 ps figure
Finite-dimensional analogs of string s <-> t duality and pentagon equation
We put forward one of the forms of functional pentagon equation (FPE), known
from the theory of integrable models, as an algebraic explanation to the
phenomenon known in physics as st duality. We present two simple geometrical
examples of FPE solutions, one of them yielding in a particular case the
well-known Veneziano expression for 4-particle amplitude. Finally, we interpret
our solutions of FPE in terms of relations in Lie groups.Comment: LaTeX, 12 pages, 6 eps figure
One-dimensional semirelativity for electrons in carbon nanotubes
It is shown that the band structure of single-wall semiconducting carbon
nanotubes (CNT) is analogous to relativistic description of electrons in
vacuum, with the maximum velocity = cm/s replacing the light velocity.
One-dimensional semirelativistic kinematics and dynamics of electrons in CNT is
formulated. Two-band k.p Hamiltonian is employed to demonstrate that electrons
in CNT experience a Zitterbewegung (trembling motion) in absence of external
fields. This Zitterbewegung should be observable much more easily in CNT than
its analogue for free relativistic electrons in vacuum.Comment: 4 pages no figure
Donut and dynamic polarization effects in proton channeling through carbon nanotubes
We investigate the angular and spatial distributions of protons of the energy
of 0.223 MeV after channeling through an (11,~9) single-wall carbon nanotube of
the length of 0.2 m. The proton incident angle is varied between 0 and 10
mrad, being close to the critical angle for channeling. We show that, as the
proton incident angle increases and approaches the critical angle for
channeling, a ring-like structure is developed in the angular distribution -
donut effect. We demonstrate that it is the rainbow effect. When the proton
incident angle is between zero and a half of the critical angle for channeling,
the image force affects considerably the number and positions of the maxima of
the angular and spatial distributions. However, when the proton incident angle
is close to the critical angle for channeling, its influence on the angular and
spatial distributions is reduced strongly. We demonstrate that the increase of
the proton incident angle can lead to a significant rearrangement of the
propagating protons within the nanotube. This effect may be used to locate
atomic impurities in nanotubes as well as for creating nanosized proton beams
to be used in materials science, biology and medicine.Comment: 17 pages, 14 figure
Collective Modes of Massive Dirac Fermions in Armchair Graphene Nanoribbons
We report the plasmon dispersion characteristics of intrinsic and extrinsic
armchair graphene nanoribbons of atomic width N = 5 using a p_z-orbital tight
binding model with third-nearest-neighbor (3nn) coupling. The coupling
parameters are obtained by fitting the 3nn dispersions to that of an extended
Huckel theory. The resultant massive Dirac Fermion system has a band gap E_g
\approx 64 meV. The extrinsic plasmon dispersion relation is found to approach
a common dispersion curve as the chemical potential increases, whereas
the intrinsic plasmon dispersion relation is found to have both energy and
momentum thresholds. We also report an analytical model for the extrinsic
plasmon group velocity in the q \rightarrow 0 limit
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