2,876 research outputs found
Coexistence of double-Q spin density wave and multi-Q pair density wave in cuprate oxide superconductors
Spatial 4a x 4a modulations, with a the lattice constant of CuO_2 planes, or
the so called checkerboards can arise from double-Q spin density wave (SDW)
with Q_1 = (pm pi/a, pm 3 pi/4a) and Q_2 = (pm 3 pi/4a, pm pi/a). When multi-Q
pair density wave, that is, the condensation of d gamma-wave Cooper pairs with
zero total momenta, pm 2Q_1, pm 2Q_2, pm 4Q_1, pm 4Q_2, and so on is induced by
the SDW, gaps can have fine structures similar to those of the so called
zero-temperature pseudogaps.Comment: 4 pages, 3 figure
Theory of Kondo lattices and its application to high-temperature superconductivity and pseudo-gaps in cuprate oxides
A theory of Kondo lattices is developed for the t-J model on a square
lattice. The spin susceptibility is described in a form consistent with a
physical picture of Kondo lattices: Local spin fluctuations at different sites
interact with each other by a bare intersite exchange interaction, which is
mainly composed of two terms such as the superexchange interaction, which
arises from the virtual exchange of spin-channel pair excitations of electrons
across the Mott-Hubbard gap, and an exchange interaction arising from that of
Gutzwiller's quasi-particles. The bare exchange interaction is enhanced by
intersite spin fluctuations developed because of itself. The enhanced exchange
interaction is responsible for the development of superconducting fluctuations
as well as the Cooper pairing between Gutzwiller's quasi-particles. On the
basis of the microscopic theory, we develop a phenomenological theory of
low-temperature superconductivity and pseudo-gaps in the under-doped region as
well as high-temperature superconductivity in the optimal-doped region.
Anisotropic pseudo-gaps open mainly because of d\gamma-wave superconducting
low-energy fluctuations: Quasi-particle spectra around (\pm\pi/a,0) and
(0,\pm\pi/a), with a the lattice constant, or X points at the chemical
potential are swept away by strong inelastic scatterings, and quasi-particles
are well defined only around (\pm\pi/2a,\pm\pi/2a) on the Fermi surface or
line. As temperatures decrease in the vicinity of superconducting critical
temperatures, pseudo-gaps become smaller and the well-defined region is
extending toward X points. The condensation of d\gamma-wave Cooper pairs
eventually occurs at low enough temperatures when the pair breaking by
inelastic scatterings becomes small enough.Comment: 15 pages, 14 figure
Magnetic and charge structures in itinerant-electron magnets: Coexistence of multiple SDW and CDW
A theory of Kondo lattices is applied to studying possible magnetic and
charge structures of itinerant-electron antiferromagnets. Even helical spin
structures can be stabilized when the nesting of the Fermi surface is not sharp
and the superexchange interaction, which arises from the virtual exchange of
pair excitations across the Mott-Hubbard gap, is mainly responsible for
magnetic instability. Sinusoidal spin structures or spin density waves (SDW)
are only stabilized when the nesting of the Fermi surface is sharp enough and a
novel exchange interaction arising from that of pair excitations of
quasi-particles is mainly responsible for magnetic instability. In particular,
multiple SDW are stabilized when their incommensurate ordering wave-numbers
are multiple; magnetizations of different components
are orthogonal to each other in double and triple SDW when magnetic anisotropy
is weak enough. Unless are commensurate, charge density waves
(CDW) with coexist with SDW with . Because the
quenching of magnetic moments by the Kondo effect depends on local numbers of
electrons, the phase of CDW or electron densities is such that magnetic moments
are large where the quenching is weak. It is proposed that the so called stipe
order in cuprate-oxide high-temperature superconductors must be the coexisting
state of double incommensurate SDW and CDW.Comment: 10 pages, no figure
Frustrated electron liquids in the Hubbard model
The ground state of the Hubbard model is studied within the constrained
Hilbert space where no order parameter exists. The self-energy of electrons is
decomposed into the single-site and multisite self-energies. The calculation of
the single-site self-energy is mapped to a problem of self-consistently
determining and solving the Anderson model. When an electron reservoir is
explicitly considered, it is proved that the single-site self-energy is that of
a normal Fermi liquid even if the multisite self-energy is anomalous. Thus, the
ground state is a normal Fermi liquid in the supreme single-site approximation
(S^3A). In the strong-coupling regime, the Fermi liquid is stabilized by the
Kondo effect in the S^3A and is further stabilized by the Fock-type term of the
superexchange interaction or the resonating-valence-bond (RVB) mechanism beyond
the S^3A. The stabilized Fermi liquid is frustrated as much as an RVB spin
liquid in the Heisenberg model. It is a relevant unperturbed state that can be
used to study a normal or anomalous Fermi liquid and an ordered state in the
whole Hilbert space by Kondo lattice theory. Even if higher-order multisite
terms than the Fock-type term are considered, the ground state cannot be a Mott
insulator. It can be merely a gapless semiconductor even if the multisite
self-energy is so anomalous that it is divergent at the chemical potential. A
Mott insulator is only possible as a high temperature phase.Comment: 11 pages, no figur
Thermal conductivity of the thermoelectric layered cobalt oxides measured by the Harman method
In-plane thermal conductivity of the thermoelectric layered cobalt oxides has
been measured using the Harman method, in which thermal conductivity is
obtained from temperature gradient induced by applied current. We have found
that the charge reservoir block (the block other than the CoO block)
dominates the thermal conduction, where a nano-block integration concept is
effective for material design. We have further found that the thermal
conductivity shows a small but finite in-plane anisotropy between and
axes, which can be ascribed to the misfit structure.Comment: 4 pages, 4 figures, J. Appl. Phys. (scheduled on July 1, 2004
Valley Splitting Theory of SiGe/Si/SiGe Quantum Wells
We present an effective mass theory for SiGe/Si/SiGe quantum wells, with an
emphasis on calculating the valley splitting. The theory introduces a valley
coupling parameter, , which encapsulates the physics of the quantum well
interface. The new effective mass parameter is computed by means of a tight
binding theory. The resulting formalism provides rather simple analytical
results for several geometries of interest, including a finite square well, a
quantum well in an electric field, and a modulation doped two-dimensional
electron gas. Of particular importance is the problem of a quantum well in a
magnetic field, grown on a miscut substrate. The latter may pose a numerical
challenge for atomistic techniques like tight-binding, because of its
two-dimensional nature. In the effective mass theory, however, the results are
straightforward and analytical. We compare our effective mass results with
those of the tight binding theory, obtaining excellent agreement.Comment: 13 pages, 7 figures. Version submitted to PR
Resonant X-Ray Scattering from the Quadrupolar Ordering Phase of CeB_6
We theoretically investigate the origin of the resonant x-ray scattering
(RXS) signal near the Ce absorption edge in the quadrupolar ordering
phase of CeB, considering the intersite interaction between the
states in the initial state. The anisotropic charge distribution of the
states modulates the states through the intra-atomic Coulomb interaction
and thereby generates a large RXS superlattice intensity. The temperature and
magnetic field dependence indicates that the induced dipolar and octupolar
orders have little influence on the RXS spectra, in good agreement with the
recent experiment.Comment: 4 pages, 4 figure
A novel human hair protein fiber prepared by watery hybridization spinning
This is a preprint of an article published in [Hirao, Y; Ohkawa, K; Yamamoto, H; Fujii, T.,A novel human hair protein fiber prepared by watery hybridization spinning,MACROMOLECULAR MATERIALS AND ENGINEERING,Vol 290,165-171(2005)]ArticleMACROMOLECULAR MATERIALS AND ENGINEERING. 290(3): 165-171 (2005)journal articl
Alkaline phosphatase encapsulated in gellan-chitosan hybrid capsules
This is a preprint of an article published in [Fujii, T; Ogiwara, D; Ohkawa, K; Yamamoto, H.,Alkaline phosphatase encapsulated in gellan-chitosan hybrid capsules,MACROMOLECULAR BIOSCIENCE,Vol 5,394-400(2005)]ArticleMACROMOLECULAR BIOSCIENCE. 5(5): 394-400 (2005)journal articl
Theory of itinerant-electron ferromagnetism
A theory of Kondo lattices or a expansion theory, with spatial
dimensionality, is applied to studying itinerant-electron ferromagnetism. Two
relevant multi-band models are examined: a band-edge model where the chemical
potential is at one of band-edges, the top or bottom of bands, and a flat-band
model where one of bands is almost flat or dispersionless and the chemical
potential is at the flat band. In both the models, a novel ferromagnetic
exchange interaction arises from the virtual exchange of pair excitations of
quasiparticles; it has two novel properties such as its strength is in
proportion to the effective Fermi energy of quasiparticles and its temperature
dependence is responsible for the Curie-Weiss law. When the Hund coupling
is strong enough, the superexchange interaction, which arises from the virtual
exchange of pair excitations of electrons across the Mott-Hubbard gap, is
ferromagnetic. In particular, it is definitely ferromagnetic for any nonzero
in the large limit of band multiplicity. Ferromagnetic instability
occurs, when the sum of the two exchange interactions is ferromagnetic and it
overcomes the quenching of magnetic moments by the Kondo effect or local
quantum spin fluctuations and the suppression of magnetic instability by the
mode-mode coupling among intersite spin fluctuations.Comment: 14 pages, 4 figure
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