933 research outputs found
Excitonic Bound State in the Extended Anderson Model with c-f Coulomb Interaction
The Anderson model with the Coulomb interaction between the local and
conduction electrons is studied in the semiconducting phase. Based on a
perturbation theory from the atomic limit, leading contributions for the c-f
Coulomb interaction are incorporated as a vertex correction to hybridization.
An analytical solution shows that the effective attraction in the intermediate
states leads to a bound state localized at the local electron site.
Self-consistent equations are constructed as an extension of the non-crossing
approximation (NCA) to include the vertex part yielding the bound state. A
numerical calculation demonstrates the excitonic bound state inside the
semiconducting gap for single-particle excitations, and a discontinuity at the
gap edge for magnetic excitations.Comment: 15 pages, 20 figures, submitted to J. Phys. Soc. Jp
Effect of Disorder on Fermi surface in Heavy Electron Systems
The Kondo lattice model with substitutional disorder is studied with
attention to the size of the Fermi surface and the associated Dingle
temperature. The model serves for understanding heavy-fermion Ce compounds
alloyed with La according to substitution Ce{x}La{1-x}. The Fermi surface is
identified from the steepest change of the momentum distribution of conduction
electrons, and is derived at low enough temperature by the dynamical mean-field
theory (DMFT) combined with the coherent potential approximation (CPA). The
Fermi surface without magnetic field increases in size with decreasing x from
x=1 (Ce end), and disappears at such x that gives the same number of localized
spins as that of conduction electrons. From the opposite limit of x=0 (La end),
the Fermi surface broadens quickly as x increases, but stays at the same
position as that of the La end. With increasing magnetic field, a metamagnetic
transition occurs, and the Fermi surface above the critical field changes
continuously across the whole range of x. The Dingle temperature takes a
maximum around x=0.5. Implication of the results to experimental observation is
discussed.Comment: 5 pages, 5 figure
Explosive nucleosynthesis in core-collapse supernovae
The specific mechanism and astrophysical site for the production of half of
the elements heavier than iron via rapid neutron capture (r-process) remains to
be found. In order to reproduce the abundances of the solar system and of the
old halo stars, at least two components are required: the heavy r-process
nuclei (A>130) and the weak r-process which correspond to the lighter heavy
nuclei (A<130). In this work, we present nucleosynthesis studies based on
trajectories of hydrodynamical simulations for core-collapse supernovae and
their subsequent neutrino-driven winds. We show that the weak r-process
elements can be produced in neutrino-driven winds and we relate their
abundances to the neutrino emission from the nascent neutron star. Based on the
latest hydrodynamical simulations, heavy r-process elements cannot be
synthesized in the neutrino-driven winds. However, by artificially increasing
the wind entropy, elements up to A=195 can be made. In this way one can mimic
the general behavior of an ejecta where the r-process occurs. We use this to
study the impact of the nuclear physics input (nuclear masses, neutron capture
cross sections, and beta-delayed neutron emission) and of the long-time
dynamical evolution on the final abundances.Comment: 10 pages, 8 figures, invited talk, INPC 2010 Vancouver, Journal of
Physics: Conference Serie
Realization of Heavy Local Fermi Liquid and Non-Fermi Liquid in f Crystalline-Electric-Field Singlet-Triplet Configuration
Using the numerical renormalization group method, we investigate an extended
Anderson model, in which correlated electrons with the
(singlet)-(triplet) f crystalline-electric-field (CEF)
configuration hybridize with conduction electrons of (doublet) and
(quartet) under cubic symmetry, from a strong spin-orbit
interaction limit. For the case of the parameters relevant to PrFe4P12, the
system is under competition between the CEF singlet fixed point and the
multichannel
Kondo non-Fermi liquid fixed point arising from the quadrupolar coupling
between the impurity with pseudospin 1 and the conduction electron with
pseudospin 3/2 . We consider that this result reveals the origin of the
heaviness of the effective mass and non-Fermi liquid behavior of the Pr- based
filled skutterudite compounds.Comment: 9 pages, 5 figure
Baryogenesis and CP-Violating Domain Walls in the Background of a Magnetic Field
Within the domain wall-mediated electroweak baryogenesis, we study fermion
scattering off a CP-violating wall in the background of an uniform magnetic
field. In particular, we calculate the asymmetry between the reflection
coefficients for right-handed and left-handed chiral fermions, \Delta R = R_{R
\to L} - R_{L \to R}, which is of relevance to non local baryogenesis
mechanisms.Comment: replaced with revised conclusion version, to be published in JCA
Fermion Scattering off CP-Violating Electroweak Bubble Wall
A general prescription to solve the Dirac equation in the presence of
CP-violating electroweak bubble wall is presented. The profile of the bubble
wall is not specified except that the wall height is and zero deep in the
broken- and the symmetric-phase regions, respectively, where is a fermion
mass given by the Higgs-vacuum-expectation value and the Yukawa coupling. The
CP-violating effects are evaluated by regarding CP-violating part of the bubble
wall as a perturbation to CP-conserving solutions. The basic quantity,
, which would contribute to the
cosmological baryon asymmetry, is estimated for some typical profiles of the
wall, where () is the reflection
coefficient of right-handed chiral fermion (anti-fermion).Comment: 30 pages, 2 figures ( uuencoded tar.Z file of PS files is appended ),
plain TeX with phyzzx, tables and epsf,SAGA-HE-55--KYUSHU-HET-1
Vortex jamming in superconductors and granular rheology
We demonstrate that a highly frustrated anisotropic Josephson junction
array(JJA) on a square lattice exhibits a zero-temperature jamming transition,
which shares much in common with those in granular systems. Anisotropy of the
Josephson couplings along the horizontal and vertical directions plays roles
similar to normal load or density in granular systems. We studied numerically
static and dynamic response of the system against shear, i. e. injection of
external electric current at zero temperature. Current-voltage curves at
various strength of the anisotropy exhibit universal scaling features around
the jamming point much as do the flow curves in granular rheology, shear-stress
vs shear-rate. It turns out that at zero temperature the jamming transition
occurs right at the isotropic coupling and anisotropic JJA behaves as an exotic
fragile vortex matter : it behaves as superconductor (vortex glass) into one
direction while normal conductor (vortex liquid) into the other direction even
at zero temperature. Furthermore we find a variant of the theoretical model for
the anisotropic JJA quantitatively reproduces universal master flow-curves of
the granular systems. Our results suggest an unexpected common paradigm
stretching over seemingly unrelated fields - the rheology of soft materials and
superconductivity.Comment: 10 pages, 5 figures. To appear in New Journal of Physic
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