48,257 research outputs found
Relationship between single-particle excitation and spin excitation at the Mott Transition
An intuitive interpretation of the relationship between the dispersion
relation of the single-particle excitation in a metal and that of the spin
excitation in a Mott insulator is presented, based on the results for the one-
and two-dimensional Hubbard models obtained by using the Bethe ansatz,
dynamical density-matrix renormalization group method, and cluster perturbation
theory. The dispersion relation of the spin excitation in the Mott insulator is
naturally constructed from that of the single-particle excitation in the
zero-doping limit in both one- and two-dimensional Hubbard models, which allows
us to interpret the doping-induced states as the states that lose charge
character toward the Mott transition. The characteristic feature of the Mott
transition is contrasted with the feature of a Fermi liquid and that of the
transition between a band insulator and a metal.Comment: 6 pages, 2 figures, to appear in JPS Conf. Pro
Several different gas-liquid contactors utilizing centrifugal force
Gas-liquid contactors utilizing centrifugal forc
Mesoscopic conductance fluctuations in a coupled quantum dot system
We study the transport properties of an Aharonov-Bohm ring containing two
quantum dots. One of the dots has well-separated resonant levels, while the
other is chaotic and is treated by random matrix theory. We find that the
conductance through the ring is significantly affected by mesoscopic
fluctuations. The Breit-Wigner resonant peak is changed to an antiresonance by
increasing the ratio of the level broadening to the mean level spacing of the
random dot. The asymmetric Fano form turns into a symmetric one and the
resonant peak can be controlled by magnetic flux. The conductance distribution
function clearly shows the influence of strong fluctuations.Comment: 4 pages, 4 figures; revised for publicatio
The possible role of stellar mergers for the formation of multiple stellar populations in globular clusters
Many possible scenarios for the formation of multiple stellar populations (MSP) in globular clusters (GCs) have been discussed so far, including the involvement of asymptotic giant branch stars, fast rotating main sequence stars, very massive main sequence stars and mass-transferring massive binaries based on stellar evolution modelling. But self-consistent, dynamical simulations of very young GCs are usually not considered. In this work, we perform direct -body modelling such systems with total masses up to M, taking into account the observationally constrained primordial binary properties, and discuss the stellar-mergers driven both by binary stellar evolution and dynamical evolution of GCs. The occurrence of stellar mergers is enhanced significantly in binary-rich clusters such that stars forming from the gas polluted by mergers-driven ejection/winds would appears as MSPs. We thus emphasize that stellar mergers can be an important process that connects MSP formation with star cluster dynamics, and that multiple MSP formation channels can naturally work together. The scenario studied here, also in view of a possible top-heavy IMF, may be particularly relevant for explaining the high mass fraction of MSPs (the mass budget problem) and the absence of MSPs in young and low-mass star clusters
An ab initio study of 3s core-level x-ray photoemission spectra in transition metals
We calculate the - and -core-level x-ray photoemission spectroscopy
(XPS) spectra in the ferromagnetic and nonmagnetic transition metals by
developing an \emph{ab initio} method. We obtain the spectra exhibiting the
characteristic shapes as a function of binding energy in good agreement with
experimental observations. The spectral shapes are strikingly different between
the majority spin channel and the minority spin channel for ferromagnetic
metals Ni, Co, and Fe, that is, large intensities appear in the higher binding
energy side of the main peak (satellite) in the majority spin channel. Such
satellite or shoulder intensities are also obtained for nonmagnetic metals V
and Ru. These behaviors are elucidated in terms of the change of the
one-electron states induced by the core-hole potential.Comment: 11 pages, 12 figures, to appear in Phys. Rev.
Trans-Magnetosonic Accretion in a Black Hole Magnetosphere
We present the critical conditions for hot trans-fast magnetohydrodynamical
(MHD) flows in a stationary and axisymmetric black-hole magnetosphere. To
accrete onto the black hole, the MHD flow injected from a plasma source with
low velocity must pass through the fast magnetosonic point after passing
through the ``inner'' or ``outer'' Alfven point. We find that a trans-fast MHD
accretion solution related to the inner Alfven point is invalid when the
hydrodynamical effects on the MHD flow dominate at the magnetosonic point,
while the other accretion solution related to the outer Alfven point is invalid
when the total angular momentum of the MHD flow is seriously large. When both
regimes of the accretion solutions are valid in the black hole magnetosphere,
we can expect the transition between the two regimes. The variety of these
solutions would be important in many highly energetic astrophysical situations.Comment: 27 pages, 12 figures, accepted to Ap
The effect of supersymmetry breaking in the Mass Varying Neutrinos
We discuss the effect of the supersymmetry breaking on the Mass Varying
Neutrinos(MaVaNs) scenario. Especially, the effect mediated by the
gravitational interaction between the hidden sector and the dark energy sector
is studied. A model including a chiral superfield in the dark sector and the
right handed neutrino superfield is proposed. Evolutions of the neutrino mass
and the equation of state parameter are presented in the model. It is remarked
that only the mass of a sterile neutrino is variable in the case of the
vanishing mixing between the left-handed and a sterile neutrino on cosmological
time scale. The finite mixing makes the mass of the left-handed neutrino
variable.Comment: 6 pages, 7 figures, RevTeX4, references added, discussions and
figures revise
Biquadratic antisymmetric exchange and the magnetic phase diagram of magnetoelectric CuFeO
Biquadratic {\it antisymmetric} exchange terms of the form , where is the
unit vector connecting sites and and , due partially to
magnetoelectric coupling effects, are shown to be responsible for the spin-flop
helical phase in CuFeO at low magnetic field and temperature. Usual
biquadratic {\it symmetric} exchange, likely due to magnetoelastic coupling, is
found to support the stability of axial magnetic states at higher fields in
this nearly-Heisenberg like stacked triangular antiferromagnet. A model
Hamiltonian which also includes substantial interplane and higher-neighbor
intraplane exchange interactions, reproduces the unique series of observed
commensurate and incommensurate periodicity phases with increasing applied
magnetic field in this highly frustrated system. The magnetic field-temperature
phase diagram is discussed in terms of a Landau-type free energy.Comment: 7 pages, 9 figure
Theory of resonant inelastic x-ray scattering at the K edge in LaCuO - Multiple scattering effects -
We develop a theory of resonant inelastic x-ray scattering (RIXS) at the
edge in LaCuO on the basis of the Keldysh Green's function formalism.
In our previous analysis (Phys. Rev. B 71, 035110 (2005)), the scattering by
the core-hole potential was treated within the Born approximation, and a
crude-model density of states was used for the band. We improve the
analysis by taking account of the multiple scattering in Cu3d-O bands and
by using a realistic DOS obtained from a band calculation. The multiple
scattering effect is evaluated with the use of the time representation
developed by Nozi\`eres and De Dominicis. It is found that the multiple
scattering effect makes the -edge peak in the absorption coefficient shift
to the lower energy region as a function of photon energy, that is, the photon
energy required to excite the electron to the -edge peak reduces. It is
also found that the multiple-scattering effect does not change the two-peak
structure in the RIXS spectra but modifies slightly the shape as a function of
energy loss. These findings suggests that the multiple scattering effect could
mainly be included into a renormalization of the core-level energy and partly
justify the Born approximation, leading to a future application to the RIXS in
three-dimensional systems.Comment: revised version with extended discussion, 24 pages, 12 figures,
accepted for PR
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