8,958 research outputs found
Electronic States and Superconducting Transition Temperature based on the Tomonaga-Luttinger liquid in PrBaCuO
An NQR experiment revealed superconductivity of
PrBaCuO (Pr247) to be realized on CuO double chain
layers and suggests possibility of novel one-dimensional(1D) superconductivity.
To clarify the nature of the 1D superconductivity, we calculate the band
dispersions of Pr247 by using the generalized gradient approximation(GGA). It
indicates that Fermi surface of CuO double chains is well described to the
electronic structure of a quasi-1D system.
Assuming the zigzag Hubbard chain model to be an effective model of the
system, we derive tight binding parameters of the model from a fit to the
result of GGA. Based on the Tomonaga-Luttinger liquid theory, we estimate
transition temperature () of the quasi-1D zigzag Hubbard model from the
calculated value of the Luttinger liquid parameter . The result of
is consistent with that of experiments in Pr247 and it suggests that the
mechanism of the superconductivity is well understood within the concept of the
Tomonaga-Luttinger liquid.Comment: 4 pages, 5 figure
Superconductivity of the One-Dimensional d-p Model with p-p transfer
Using the numerical diagonalization method, we investigate the
one-dimensional - model, simulating a Cu-O linear chain with strong
Coulomb repulsions. Paying attention to the effect of the transfer energy
between the nearest neighbor oxygen-sites, we calculate the critical
exponent of correlation functions based on the Luttinger liquid
relations and the ground state energy as a function of an external
flux . We find that the transfer increases the charge
susceptibility and the exponent in cooperation with the repulsion
at Cu-site. We also show that anomalous flux quantization occurs for
. The superconducting region is presented on a phase diagram of
vs. plane.Comment: 4 pages, RevTex + 5 PS figures include
Superconductivity in a Two-Orbital Hubbard Model with Electron and Hole Fermi Pockets: Application in Iron Oxypnictide Superconductors
We investigate the electronic states of a one-dimensional two-orbital Hubbard
model with band splitting by the exact diagonalization method. The Luttinger
liquid parameter is calculated to obtain superconducting (SC) phase
diagram as a function of on-site interactions: the intra- and inter-orbital
Coulomb and , the Hund coupling , and the pair transfer . In
this model, electron and hole Fermi pockets are produced when the Fermi level
crosses both the upper and lower orbital bands. We find that the system shows
two types of SC phases, the SC \Roman{u'-large} for and the SC
\Roman{u-large} for , in the wide parameter region including both weak
and strong correlation regimes. Pairing correlation functions indicate that the
most dominant pairing for the SC \Roman{u'-large} (SC \Roman{u-large}) is the
intersite (on-site) intraorbital spin-singlet with (without) sign reversal of
the order parameters between two Fermi pockets. The result of the SC
\Roman{u'-large} is consistent with the sign-reversing s-wave pairing that has
recently been proposed for iron oxypnictide superconductors.Comment: 5 pages, 8 figures, to appear in J. Phys. Soc. Jpn., Vol.78, No.12,
p.12470
Elastic Convection in Vibrated Viscoplastic Fluids
We observe a new type of behavior in a shear thinning yield stress fluid:
freestanding convection rolls driven by vertical oscillation. The convection
occurs without the constraint of container boundaries yet the diameter of the
rolls is spontaneously selected for a wide range of parameters. The transition
to the convecting state occurs without hysteresis when the amplitude of the
plate acceleration exceeds a critical value. We find that a non-dimensional
stress, the stress due to the inertia of the fluid normalized by the yield
stress, governs the onset of the convective motion.Comment: 4 pages, 6 figure
Saturation of Magnetorotational Instability through Magnetic Field Generation
The saturation mechanism of Magneto-Rotational Instability (MRI) is examined
through analytical quasilinear theory and through nonlinear computation of a
single mode in a rotating disk. We find that large-scale magnetic field is
generated through the alpha effect (the correlated product of velocity and
magnetic field fluctuations) and causes the MRI mode to saturate. If the
large-scale plasma flow is allowed to evolve, the mode can also saturate
through its flow relaxation. In astrophysical plasmas, for which the flow
cannot relax because of gravitational constraints, the mode saturates through
field generation only.Comment: 9 pages, 10 figures to appear in ApJ, Jun 2009, 10 v69
Lymph node removal enhances corneal graft survival in mice at high risk of rejection
Peer reviewedPublisher PD
Effect of Quantum Fluctuations on Magnetic Ordering in CaVO
We present a theoretical model for CaVO: the -depleted square
spin- Heisenberg model which includes both the nearest-neighbor coupling
() and the next-nearest-neighbor coupling (), where and are
antiferromagnetic. Recent experiments of the neutron diffraction by Harashina
et.al. report the magnetic ordering at low temperatures, which may be called as
a stripe phase. It is shown that the observed spin structure is not stable in
the classical theory. By employing the modified spin wave theory, we show that
the stripe phase is stabilized by the quantum fluctuations for .
In CaVO, the coupling constants are estimated as by
comparing the theoretical and experimental results.Comment: submitted to J. Phys. Soc. Jp
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