5,609 research outputs found
Specific Heat and Superfluid Density for Possible Two Different Superconducting States in NaxCoO2.yH2O
Several thermodynamic measurements for the cobaltate superconductor,
NaxCoO2.yH2O, have so far provided results inconsistent with each other. In
order to solve the discrepancies, we microscopically calculate the temperature
dependences of specific heat and superfluid density for this superconductor. We
show that two distinct specific-heat data from Oeschler et al. and Jin et al.
are reproduced, respectively, for the extended s-wave state and the p-wave
state. Two different superfluid-density data are also reproduced for each case.
These support our recent proposal of possible two different pairing states in
this material. In addition, we discuss the experimentally proposed large
residual Sommerfeld coefficient and extremely huge effective carrier mass.Comment: 5 pages, 4 figures, Submitted to J. Phys. Soc. Jp
Ferromagnetic fluctuation and possible triplet superconductivity in Na_xCoO_2*yH_2O: Fluctuation-exchange study of multi-orbital Hubbard model
Spin and charge fluctuations and superconductivity in a recently discovered
superconductor Na_xCoO_2*yH_2O are studied based on a multi-orbital Hubbard
model. Tight-binding parameters are determined to reproduce the LDA band
dispersions with the Fermi surface, which consist of a large cylindrical one
around the Gamma-point and six hole pockets near the K-points. By applying the
fluctuation-exchange (FLEX) approximation, we show that the Hund's-rule
coupling between the Co t2g orbitals causes ferromagnetic (FM) spin
fluctuation. Triplet f_{y(y^2-3x^2)}-wave and p-wave pairings are favored by
this FM fluctuation on the hole-pocket band. We propose that, in
Na_xCoO_2*yH_2O, the Co t2g orbitals and inter-orbital Hund's-rule coupling
play important roles on the triplet pairing, and this compound can be a first
example of the triplet superconductor in which the orbital degrees of freedom
play substantial roles.Comment: 5 pages, 3 figure
Hall effect of spin-chirality origin in a triangular-lattice helimagnet Fe1.3Sb
We report on a topological Hall effect possibly induced by scalar spin
chirality in a quasi-two- dimensional helimagnet FeSb. In the
low-temperature region where the spins on interstitial- Fe (concentration
) intervening the spin-ordered triangular planes tend to
freeze, a non-trivial component of Hall resistivity with opposite sign of the
conventional anomalous Hall term is observed under magnetic field applied
perpendicular to the triangular-lattice plane. The observed unconventional Hall
effect is ascribed to the scalar spin chirality arising from the heptamer
spin-clusters around the interstitial-Fe sites, which can be induced by the
spin modulation by the Dzyaloshinsky-Moriya interaction
CoO2-Layer-Thickness Dependence of Magnetic Properties and Possible Two Different Superconducting States in NaxCoO2.yH2O
In order to understand the experimentally proposed phase diagrams of
NaxCoO2.yH2O, we theoretically study the CoO2-layer-thickness dependence of
magnetic and superconducting (SC) properties by analyzing a multiorbital
Hubbard model using the random phase approximation. When the Co valence (s) is
+3.4, we show that the magnetic fluctuation exhibits strong layer-thickness
dependence where it is enhanced at finite (zero) momentum in the thicker
(thinner) layer system. A magnetic order phase appears sandwiched by two SC
phases, consistent with the experiments. These two SC phases have different
pairing states where one is the singlet extended s-wave state and the other is
the triplet p-wave state. On the other hand, only a triplet p-wave SC phase
with dome-shaped behavior of Tc is predicted when s=+3.5, which is also
consistent with the experiments. Controversial experimental results on the
magnetic properties are also discussed.Comment: 5 pages, 4 figures. Submitted to Journal of the Physical Society of
Japa
Roles of Bond Alternation in Magnetic Phase Diagram of RMnO3
In order to investigate nature of the antiferromagnetic structures in
perovskite RMnO3, we study a Heisenberg J1-J2 model with bond alternation using
analytical and numerical approaches. The magnetic phase diagram which includes
incommensurate spiral states and commensurate collinear states is reproduced.
We discuss that the magnetic structure with up-up-down-down spin configuration
(E-type structure) and the ferroelectricity emerge cooperatively to stabilize
this phase. Magnetoelastic couplings are crucial to understand the magnetic and
electric phase diagram of RMnO3.Comment: 5 pages, 6 figure
Dynamics of Multiferroic Domain Wall in Spin-Cycloidal Ferroelectric DyMnO
We report the dielectric dispersion of the giant magnetocapacitance (GMC) in
multiferroic DyMnO over a wide frequency range. The GMC is found to be
attributable not to the softened electromagnon but to the electric-field-driven
motion of multiferroic domain wall (DW). In contrast to conventional
ferroelectric DWs, the present multiferroic DW motion holds extremely high
relaxation rate of s even at low temperatures. This
mobile nature as well as the model simulation suggests that the multiferroic DW
is not atomically thin as in ferroelectrics but thick, reflecting its magnetic
origin.Comment: 4 pages, 4 figure
INFLUENCE OF DIFFERENT SHOULDER ABDUCTION ANGLES DURING BASEBALL PlTCHING ON 'THROWING PERFORMANCE AND JOINT KINETICS
The relationships between shoulder abduction angle at ball release and wrist velocity and several injury-related kinetic parameters were investigated. Based on kinematic data of nine overhand and three-quarter-hand pitchers, several pitching motions with different shoulder abduction angles from the original were simulated. The wrist velocity and several injury-related kinetic parameters for the motion with 90 degree shoulder abduction angle at ball release were compared with those for the motions with other shoulder abduction angles. The 90 degree abduction angle maximised wrist velocity and decreased elbow joint kinetics, but did not always decrease shoulder joint kinetics
Molecular structures and vibrations of neutral and anionic CuOx (x = 1-3,6) clusters
We report equilibrium geometric structures of CuO2, CuO3, CuO6, and CuO
clusters obtained by an all-electron linear combination of atomic orbitals
scheme within the density-functional theory with generalized gradient
approximation to describe the exchange-correlation effects. The vibrational
stability of all clusters is examined on the basis of the vibrational
frequencies. A structure with Cs symmetry is found to be the lowest-energy
structure for CuO2, while a -shaped structure with C2v symmetry is the most
stable structure for CuO3. For the larger CuO6 and CuO clusters, several
competitive structures exist with structures containing ozonide units being
higher in energy than those with O2 units. The infrared and Raman spectra are
calculated for the stable optimal geometries. ~Comment: Uses Revtex4, (Better quality figures can be obtained from authors
Co-NMR Knight Shift of NaxCoO2 \dot yH2O Studied in Both Superconducting Regions of the Tc-nuQ3 Phase Diagram Divided by the Nonsuperconducting Phase
In the temperature (T)-nuQ3 phase diagram of NaxCoO2 \dot yH2O, there exist
two superconducting regions of nuQ3 separated by the nonsuperconducting region,
where nuQ3 is usually estimated from the peak position of the 59Co-NQR spectra
of the 5/2-7/2 transition and well-approximated here as nuQ3~3nuQ,nuQ being the
interaction energy between the nuclear quadrupole moment and the electric field
gradient. We have carried out measurements of the 59Co-NMR Knight shift (K) for
a single crystal in the higher-nuQ3 superconducting phase and found that K
begins to decrease with decreasing T at Tc for both magnetic field directions
parallel and perpendicular to CoO2-planes. The result indicates together with
the previous ones that the superconducting pairs are in the spin-singlet state
in both phases, excluding the possibility of the spin-triplet superconductivity
in this phase diagram. The superconductivity of this system spreads over the
wide nuQ3 regions, but is suppressed in the narrow region located at the middle
point of the region possibly due to charge instability.Comment: 8 pages, 5 figures, submitted to J. Phys. Soc. Jp
- …