10,725 research outputs found
Study of interacting electrons in graphene under the renormalized-ring-diagram approximation
Using the tight-binding model with long-range Coulomb interactions between
electrons, we study some of the electronic properties of graphene. The Coulomb
interactions are treated with the renormalized-ring-diagram approximation. By
self-consistently solving the integral equations for the Green function, we
calculate the spectral density. The obtained result is in agreement with
experimental observation. In addition, we also compute the density of states,
the distribution functions, and the ground-state energy. Within the present
approximation, we find that the imaginary part of the self-energy fixed at the
Fermi momentum varies as quadratic in energy close to the chemical potential,
regardless the system is doped or not. This result appears to indicate that the
electrons in graphene always behave like a moderately correlated Fermi liquid.Comment: 11 pages, 13 figure
Spin dynamics in the antiferromagnetic phase for electron-doped cuprate superconductors
Based on the --- model we have calculated the dynamical spin
susceptibilities in the antiferromagnetic (AF) phase for electron-doped
cuprates, by use of the slave-boson mean-field theory and random phase
approximation. Various results for the susceptibilities versus energy and
momentum have been shown at different dopings. At low energy, except the
collective spin-wave mode around and 0, we have primarily observed
that new resonance peaks will appear around and equivalent
points with increasing doping, which are due to the particle-hole excitations
between the two AF bands. The peaks are pronounced in the transverse
susceptibility but not in the longitudinal one. These features are predicted
for neutron scattering measurements.Comment: 5 pages, 3 figures, published version with minor change
Phase diagram of doped BaFeAs superconductor under broken symmetry
We develop a minimal multiorbital tight-binding model with realistic hopping
parameters. The model breaks the symmetry of the tetragonal point group by
lowering it from to , which accurately describes the Fermi
surface evolution of the electron-doped BaFeCoAs and hole-doped
BaKFeAs compounds. An investigation of the phase diagram
with a mean-field -- Bogoliubov-de Gennes Hamiltonian results in
agreement with the experimentally observed electron- and hole-doped phase
diagram with only one set of , and parameters. Additionally, the
self-consistently calculated superconducting order parameter exhibits
-wave pairing symmetry with a small d-wave pairing admixture in the
entire doping range, % The superconducting -wave order parameter
which is the subtle result of the weakly broken symmetry and competing
interactions in the multiorbital mean-field Hamiltonian
Elastodynamics of radially inhomogeneous spherically anisotropic elastic materials in the Stroh formalism
A method is presented for solving elastodynamic problems in radially
inhomogeneous elastic materials with spherical anisotropy, i.e.\ materials such
that in a spherical coordinate system
. The time harmonic displacement field is expanded in a separation of variables form with dependence on
described by vector spherical harmonics with -dependent
amplitudes. It is proved that such separation of variables solution is
generally possible only if the spherical anisotropy is restricted to transverse
isotropy with the principal axis in the radial direction, in which case the
amplitudes are determined by a first-order ordinary differential system.
Restricted forms of the displacement field, such as ,
admit this type of separation of variables solutions for certain lower material
symmetries. These results extend the Stroh formalism of elastodynamics in
rectangular and cylindrical systems to spherical coordinates.Comment: 15 page
Perturbed Three Vortex Dynamics
It is well known that the dynamics of three point vortices moving in an ideal
fluid in the plane can be expressed in Hamiltonian form, where the resulting
equations of motion are completely integrable in the sense of Liouville and
Arnold. The focus of this investigation is on the persistence of regular
behavior (especially periodic motion) associated to completely integrable
systems for certain (admissible) kinds of Hamiltonian perturbations of the
three vortex system in a plane. After a brief survey of the dynamics of the
integrable planar three vortex system, it is shown that the admissible class of
perturbed systems is broad enough to include three vortices in a half-plane,
three coaxial slender vortex rings in three-space, and `restricted' four vortex
dynamics in a plane. Included are two basic categories of results for
admissible perturbations: (i) general theorems for the persistence of invariant
tori and periodic orbits using Kolmogorov-Arnold-Moser and Poincare-Birkhoff
type arguments; and (ii) more specific and quantitative conclusions of a
classical perturbation theory nature guaranteeing the existence of periodic
orbits of the perturbed system close to cycles of the unperturbed system, which
occur in abundance near centers. In addition, several numerical simulations are
provided to illustrate the validity of the theorems as well as indicating their
limitations as manifested by transitions to chaotic dynamics.Comment: 26 pages, 9 figures, submitted to the Journal of Mathematical Physic
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