8,724 research outputs found
An Analysis of \pi\pi-Scattering Phase Shift and Existence of \sigma(555) particle
In most of the Nambu:Jona-Lasinio(NJL)-type models, realizing the hidden
chiral symmetry, the existence of a scalar particle \sigma is needed with a
mass m_\sigma=2 m_q, as a partner of the Nambu-Goldstone boson \pi. However,
the results of many analyses on \pi\pi phase-shift thus far made have been
negative for its existence. In this paper we re-analyze the phase-shift,
applying a new method, the interfering amplitude method, which treats the
T-matrix directly and describes multi-resonances in conformity with the
unitarity. As a result, the existence of \sigma has been strongly suggested
from the behavior of the \pi\pi-->\pi\pi phase shift between the \pi\pi- and
the KK- thresholds, with mass = 553.3 +- 0.5_{st} MeV and width= 242.6 +-
1.2_{st} MeV. The most crucial point in our analysis is the introduction of a
negative background phase, possibly reflecting a ``repulsive core" in \pi\pi
interactions. The properties of f_0(980) are also investigated from data
including those over the KK threshold. Its mass is obtained as 993.2 +-
6.5_{st} +- 6.9_{sys} MeV. Its width is about a hundred MeV, although this
depends largely on the treatment of the elasticity and the \pi\pi-->KK phase
shift, both of which may have large experimental uncertainties.Comment: 22 pages, Latex with Prog. Theor. Phys. format PTPTEX.sty, 4 EPS
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Potential Profiling of the Nanometer-Scale Charge Depletion Layer in n-ZnO/p-NiO Junction Using Photoemission Spectroscopy
We have performed a depth-profile analysis of an all-oxide p-n junction diode
n-ZnO/p-NiO using photoemission spectroscopy combined with Ar-ion sputtering.
Systematic core-level shifts were observed during the gradual removal of the
ZnO overlayer, and were interpreted using a simple model based on charge
conservation. Spatial profile of the potential around the interface was
deduced, including the charge-depletion width of 2.3 nm extending on the ZnO
side and the built-in potential of 0.54 eV
Correlation between Superconducting Transition Temperature and Increase of Nuclear Spin-Lattice Relaxation Rate Devided by Temperature at in the Hydrate Cobaltate NaCoOHO
We have performed Co-nuclear quadrupole resonance (NQR) studies on
NaCoOHO compounds with different Na () and hydrate
() contents. Two samples with different Na contents but nearly the same
values ( = 0.348, = 4.7 K ; = 0.339, = 4.6 K) were
investigated. The spin-lattice relaxation rate in the superconducting
(SC) and normal states is almost the same for the two samples except just above
. NQR measurements were also performed on different-hydrate-content
samples with different values, which were prepared from the same
Na-content ( = 0.348) sample. From measurements of using the
different-hydrate-content samples, it was found that a low- sample with
K has a larger residual density of states (DOS) in the SC state and
a smaller increase of just above than a high- sample with
= 4.7 K. The former behavior is consistent with that observed in
unconventional superconductors, and the latter suggests the relationship
between and the increase in DOS just above . This increase, which is
seemingly associated with the two-dimensionality of the CoO plane, is
considered to be one of the most important factors for the occurrence of
superconductivity.Comment: 5 pages, 5 figures, To be published in J. Phys. Soc. Jp
Anisotropy in the Antiferromagnetic Spin Fluctuations of Sr2RuO4
It has been proposed that Sr_2RuO_4 exhibits spin triplet superconductivity
mediated by ferromagnetic fluctuations. So far neutron scattering experiments
have failed to detect any clear evidence of ferromagnetic spin fluctuations
but, instead, this type of experiments has been successful in confirming the
existence of incommensurate spin fluctuations near q=(1/3 1/3 0). For this
reason there have been many efforts to associate the contributions of such
incommensurate fluctuations to the mechanism of its superconductivity. Our
unpolarized inelastic neutron scattering measurements revealed that these
incommensurate spin fluctuations possess c-axis anisotropy with an anisotropic
factor \chi''_{c}/\chi''_{a,b} of \sim 2.8. This result is consistent with some
theoretical ideas that the incommensurate spin fluctuations with a c-axis
anisotropy can be a origin of p-wave superconductivity of this material.Comment: 5 pages, 3 figures; accepted for publication in PR
Unconventional Superconductivity and Nearly Ferromagnetic Spin Fluctuations in NaCoOHO
Co NQR studies were performed in recently discovered superconductor
NaCoOHO to investigate physical properties in the
superconducting (SC) and normal states. Two samples from the same NaCoO
were examined, SC bilayer-hydrate sample with K and non-SC
monolayer-hydrate sample. From the measurement of nuclear-spin lattice
relaxation rate in the SC sample, it was found that the coherence peak
is absent just below and that is proportional to temperature far
below . These results, which are in qualitatively agreement with the
previous result by Fujimoto {\it et al.}, suggest strongly that unconventional
superconductivity is realized in this compound. In the normal state,
of the SC sample shows gradual increase below 100K down to , whereas
of the non-SC sample shows the Korringa behavior in this temperature
range. From the comparison between and in the SC
sample, the increase of is attributed to nearly ferromagnetic
fluctuations. These remarkable findings suggest that the SC sample possesses
nearly ferromagnetic fluctuations, which are possibly related with the
unconventional superconductivity in this compound. The implication of this
finding is discussed.Comment: 4 pages, 5 figures. submitted to J. Phys. Soc. Jp
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