7,235 research outputs found
Theoretical study of X-ray absorption of three-dimensional topological insulator
X-ray absorption edge singularity which is usually relevant for metals is
studied for the prototype topological insulator .
The generalized integral equation of Nozi\`eres and Dominicis type for X-ray
edge singularity is derived and solved. The spin texture of surfaces states
causes a component of singularity dependent on the helicity of the spin
texture. It also yields another component for which the singularity from
excitonic processes is absent.Comment: RevTeX 4.1. 4 pages, no figur
X-ray edge singularity of bilayer graphene
The X-ray edge singularity of bilayer graphene is studied by generalizing the
path integral approach based on local action which was employed for monolayer
graphene. In sharp contrast to the case of monolayer graphene, the bilayer
graphene is found to exhibit the edge singularity even at half-filling and its
characteristics are determined by interlayer coupling. At finite bias the
singular behaviors sensitively depend on the relative magnitude of fermi energy
and applied bias, which is due to the peculiar shape of energy band at finite
bias.Comment: RevTeX 4.1, 4 pages. No figur
Parity-violating nucleon-nucleon interaction from different approaches
Two-pion exchange parity-violating nucleon-nucleon interactions from recent
effective field theories and earlier fully covariant approaches are
investigated. The potentials are compared with the idea to obtain better
insight on the role of low-energy constants appearing in the effective field
theory approach and the convergence of this one in terms of a perturbative
series. The results are illustrated by considering the longitudinal asymmetry
of polarized protons scattering off protons, , and the
asymmetry of the photon emission in radiative capture of polarized neutrons by
protons, .Comment: 31 page
Nanoscale Heat Transfer from Magnetic Nanoparticles and Ferritin in an Alternating Magnetic Field
Recent suggestions of nanoscale heat confinement on the surface of synthetic and biogenic magnetic nanoparticles during heating by radio frequency-alternating magnetic fields have generated intense interest because of the potential utility of this phenomenon for noninvasive control of biomolecular and cellular function. However, such confinement would represent a significant departure from the classical heat transfer theory. Here, we report an experimental investigation of nanoscale heat confinement on the surface of several types of iron oxide nanoparticles commonly used in biological research, using an all-optical method devoid of the potential artifacts present in previous studies. By simultaneously measuring the fluorescence of distinct thermochromic dyes attached to the particle surface or dissolved in the surrounding fluid during radio frequency magnetic stimulation, we found no measurable difference between the nanoparticle surface temperature and that of the surrounding fluid for three distinct nanoparticle types. Furthermore, the metalloprotein ferritin produced no temperature increase on the protein surface nor in the surrounding fluid. Experiments mimicking the designs of previous studies revealed potential sources of the artifacts. These findings inform the use of magnetic nanoparticle hyperthermia in engineered cellular and molecular systems
Limits on the evolution of galaxies from the statistics of gravitational lenses
We use gravitational lenses from the Cosmic Lens All-Sky Survey (CLASS) to
constrain the evolution of galaxies since redshift in the current
\LCDM cosmology. This constraint is unique as it is based on a mass-selected
lens sample of galaxies. Our method of statistical analysis is the same as in
Chae (2003). We parametrise the early-type number density evolution in the form
of and the velocity dispersion as . We find that
() if we assume , implying
that the number density of early-type galaxies is within 50% to 164% of the
present-day value at redshift . Allowing the velocity dispersion to
evolve, we find that (), indicating that
the velocity dispersion must be within 57% and 107% of the present-day value at
. These results are consistent with the early formation and passive
evolution of early-type galaxies. More stringent limits from lensing can be
obtained from future large lens surveys and by using very high-redshift quasars
(z \ga 5) such as those found from the Sloan Digital Sky Survey.Comment: 10 pages (preprint format), 2 figures, ApJL in press (December 20th
issue
Slave-boson approach to the infinite-U Anderson-Holstein impurity model
The infinite- Anderson-Holstein impurity model is studied with a focus on
the interplay between the strong electron correlation and the weak
electron-phonon interaction. The slave boson method has been employed in
combination with the large degeneracy expansion (1/N) technique. The charge and
spin susceptibilities and the phonon propagator are obtained in the
approximation scheme where the saddle point configuration and the Gaussian 1/N
fluctuations are taken into account. The spin susceptibility is found not to be
renormalized by electron-phonon interaction, while the charge susceptibility is
renormalized.
From the renormalized charge susceptibility the Kondo temperature is found to
increase by the electron-phonon interaction. It turns out that the bosonic 1/N
Gaussian fluctuations play a very crucial role, in particular, for the phonon
propagator.Comment: 12pages, 3 figures. Published in Physical Review
X-ray edge problem of graphene
The X-ray edge problem of graphene with the Dirac fermion spectrum is
studied. At half-filling the linear density of states suppresses the singular
response of the Fermi liquid, while away from half-filling the singular
features of the Fermi liquid reappear. The crossover behavior as a function of
the Fermi energy is examined in detail. The exponent of the power-law
absorption rate depends both on the intra- and inter-valley scattering, and it
changes as a function of the Fermi energy, which may be tested experimentally.Comment: 7 pages, 1 figur
Effective Potential for Uniform Magnetic Fields through Pauli Interaction
We have calculated the explicit form of the real and imaginary parts of the
effective potential for uniform magnetic fields which interact with spin-1/2
fermions through the Pauli interaction. It is found that the non-vanishing
imaginary part develops for a magnetic field stronger than a critical field,
whose strength is the ratio of the fermion mass to its magnetic moment. This
implies the instability of the uniform magnetic field beyond the critical field
strength to produce fermion pairs with the production rate density
in the
presence of Pauli interaction.Comment: 9 pages with 1 figur
Infinite Lorentz boost along the M-theory circle and non-asymptotically flat solutions in supergravities
Certain non-asymptotically flat but supersymmetric classical solution of the
type IIA supergravity can be interpreted as the infinitely-boosted version of
the D-particle solution along the M-theory circle. By a chain of T-dual
transformations, this analysis also applies to yield non-asymptotically flat
solutions from the asymptotically flat and (non)-extremal solutions with
intersecting D-strings and D five-branes of the type IIB supergravity
compactified on a five-torus. Under S-duality, the non-asymptotically flat
solutions in this context can in particular be used to describe the
(1+1)-dimensional CGHS type black holes via spontaneous compactifications.Comment: 14 pages, Revte
Instability of two-dimensional heterotic stringy black holes
We solve the eigenvalue problem of general relativity for the case of charged
black holes in two-dimensional heterotic string theory, derived by McGuigan et
al. For the case of , we find a physically acceptable
time-dependent growing mode; thus the black hole is unstable. The extremal case
is stable.Comment: 11 pages, LaTe
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