6,379 research outputs found
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
Mixing among light scalar mesons and L=1 q\bar{q} scalar mesons
Following the re-establishment of the \sigma(600) and the \kappa(900), the
light scalar mesons a_0(980) and f_0(980) together with the \sigma(600) and the
\kappa(900) are considered as the chiral scalar partner of pseudoscalar nonet
in SU(3) chiral symmetry, and the high mass scalar mesons a_0(1450),
K^*_0(1430), f_0(1370) and f_0(1710) turned out to be considered as the L=1
q\bar{q} scalar mesons. We assume that the high mass of the L=1 q\bar{q} scalar
mesons is caused by the mixing with the light scalar mesons. For the structure
of the light scalar mesons, we adopted the qq\bar{q}\bar{q} model in order to
explain the "scalar meson puzzle". The inter-mixing between the light scalar
nonet and the high mass L=1 q\bar{q} nonet and the intra-mixing among each
nonet are analyzed by including the glueball into the high mass scalar nonet.Comment: 16 pages, 5 figure
Effect of in-plane line defects on field-tuned superconductor-insulator transition behavior in homogeneous thin film
Field-tuned superconductor-insulator transition (FSIT) behavior in 2D
isotropic and homogeneous thin films is usually accompanied by a nonvanishing
critical resistance at low . It is shown that, in a 2D film including line
defects paralle to each other but with random positions perpendicular to them,
the (apparent) critical resistance in low limit vanishes, as in the 1D
quantum superconducting (SC) transition, under a current parallel to the line
defects. This 1D-like critical resistive behavior is more clearly seen in
systems with weaker point disorder and may be useful in clarifying whether the
true origin of FSIT behavior in the parent superconductor is the glass
fluctuation or the quantum SC fluctuation. As a by-product of the present
calculation, it is also pointed out that, in 2D films with line-like defects
with a long but {\it finite} correlation length parallel to the lines, a
quantum metallic behavior intervening the insulating and SC ones appears in the
resistivity curves.Comment: 16 pages, 14 figure
Evidence for Strong-coupling S-wave Superconductivity in MgB2 :11B NMR Study
We have investigated a gap structure in a newly-discovered superconductor,
MgB2 through the measurement of 11B nuclear spin-lattice relaxation rate,
^{11}(1/T_1). ^{11}(1/T_1) is proportional to the temperature (T) in the normal
state, and decreases exponentially in the superconducting (SC) state, revealing
a tiny coherence peak just below T_c. The T dependence of 1/T_1 in the SC state
can be accounted for by an s-wave SC model with a large gap size of 2\Delta
/k_BT_c \sim 5 which suggests to be in a strong-coupling regime.Comment: 2 pages with 1 figur
An embedding potential definition of channel functions
We show that the imaginary part of the embedding potential, a generalised
logarithmic derivative, defined over the interface between an electrical lead
and some conductor, has orthogonal eigenfunctions which define conduction
channels into and out of the lead. In the case of an infinitely extended
interface we establish the relationship between these eigenfunctions and the
Bloch states evaluated over the interface. Using the new channel functions, a
well-known result for the total transmission through the conductor system is
simply derived.Comment: 14 pages, 2 figure
Weak Magnetic Order in the Bilayered-hydrate NaCoOHO Structure Probed by Co Nuclear Quadrupole Resonance - Proposed Phase Diagram in Superconducting NaCoO HO
A weak magnetic order was found in a non-superconducting bilayered-hydrate
NaCoOHO sample by a Co Nuclear Quadrupole Resonance
(NQR) measurement. The nuclear spin-lattice relaxation rate divided by
temperature shows a prominent peak at 5.5 K, below which a Co-NQR peak
splits due to an internal field at the Co site. From analyses of the Co NQR
spectrum at 1.5 K, the internal field is evaluated to be 300 Oe and is
in the -plane. The magnitude of the internal field suggests that the
ordered moment is as small as using the hyperfine coupling
constant reported previously. It is shown that the NQR frequency
correlates with magnetic fluctuations from measurements of NQR spectra and
in various samples. The higher- sample has the stronger
magnetic fluctuations. A possible phase diagram in NaCoOHO is depicted using and , in which the crystal distortion
along the c-axis of the tilted CoO octahedron is considered to be a
physical parameter. Superconductivity with the highest is seemingly
observed in the vicinity of the magnetic phase, suggesting strongly that the
magnetic fluctuations play an important role for the occurrence of the
superconductivity.Comment: 5 pages, 6 figures, submitted to J. Phys. Soc. Jp
Gauged linear sigma model and pion-pion scattering
A simple gauged linear sigma model with several parameters to take the
symmetry breaking and the mass differences between the vector meson and the
axial vector meson into account is considered here as a possibly useful
template for the role of a light scalar in QCD as well as for (at a different
scale) an effective Higgs sector for some recently proposed walking technicolor
models. An analytic procedure is first developed for relating the Lagrangian
parameters to four well established (in the QCD application) experimental
inputs. One simple equation distinguishes three different cases:1. QCD with
axial vector particle heavier than vector particle, 2. possible technicolor
model with vector particle heavier than the axial vector one, 3. the unphysical
QCD case where both the KSRF and Weinberg relations hold. The model is applied
to the s-wave pion-pion scattering in QCD. Both the near threshold region and
(with an assumed unitarization) theglobal region up to about 800 MeV are
considered. It is noted that there is a little tension between the choice of
bare sigma mass parameter for describing these two regions. If a reasonable
globa fit is made, there is some loss of precision in the near threshold
region.Comment: 19 pages, 9 figure
Origin of the tetragonal-to-orthorhombic (nematic) phase transition in FeSe: a combined thermodynamic and NMR study
The nature of the tetragonal-to-orthorhombic structural transition at
K in single crystalline FeSe is studied using shear-modulus,
heat-capacity, magnetization and NMR measurements. The transition is shown to
be accompanied by a large shear-modulus softening, which is practically
identical to that of underdoped Ba(Fe,Co)As, suggesting very similar
strength of the electron-lattice coupling. On the other hand, a
spin-fluctuation contribution to the spin-lattice relaxation rate is only
observed below . This indicates that the structural, or "nematic", phase
transition in FeSe is not driven by magnetic fluctuations
Gap Symmetry an Thermal Conductivity in Nodal Superconductors
There are now many nodal superconductors in heavy fermion (HF) systems,
charge conjugated organic metals, high Tc cuprates and ruthenates. On the other
hand only few of them have a well established gap function. We present here a
study of the angular dependent thermal conductivity in the vortex state of some
of the nodal superconductors. We hope it will help to identify the nodal
directions in the gap function of UPd_2Al_3, UNi_2Al_3, UBe_13 and URu_2Si_2.Comment: 4 pages, 5 figure
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