38,915 research outputs found
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
Cloning, expression, crystallization and preliminary X-ray crystallographic analysis of a human condensin SMC2 hinge domain with short coiled coils
Kawahara, K., Nakamura, S., Katsu, Y., Motooka, D., Hosokawa, Y., Kojima, Y., Matsukawa, K., Takinowaki, H., Uchiyama, S., Kobayashi, Y., Fukui, K. & Ohkubo, T. (2010). Acta Cryst. F66, 1067-1070
The onset of magnetism peaked around x=1/4 in optimally electron-doped LnFe(1-x)Ru(x)AsO(1-y)F(y) (Ln = La, Nd or Sm) superconductors
The appearance of static magnetism, nanoscopically coexisting with
superconductivity, is shown to be a general feature of optimally electron-doped
LnFe(1-x)Ru(x)AsO(1-y)F(y) superconductor (Ln - lanthanide ion) upon isovalent
substitution of Fe by Ru. The magnetic ordering temperature T_N and the
magnitude of the internal field display a dome-like dependence on x, peaked
around x=1/4, with higher T_N values for those materials characterized by a
larger z cell coordinate of As. Remarkably, the latter are also those with the
highest superconducting transition temperature (T_c) for x=0. The reduction of
T_c(x) is found to be significant in the x region of the phase diagram where
the static magnetism develops. Upon increasing the Ru content superconductivity
eventually disappears, but only at x=0.6.Comment: accepted for publication in PR
Fast recovery of the stripe magnetic order by Mn/Fe substitution in F-doped LaFeAsO superconductors
As Nuclear Magnetic (NMR) and Quadrupolar (NQR) Resonance were used,
together with M\"{o}ssbauer spectroscopy, to investigate the magnetic state
induced by Mn for Fe substitutions in F-doped LaFeMnAsO
superconductors. The results show that % of Mn doping is enough to
suppress the superconducting transition temperature from 27 K to zero and
to recover the magnetic structure observed in the parent undoped LaFeAsO. Also
the tetragonal to orthorhombic transition of the parent compound is recovered
by introducing Mn, as evidenced by a sharp drop of the NQR frequency. The NQR
spectra also show that a charge localization process is at play in the system.
Theoretical calculations using a realistic five-band model show that
correlation-enhanced RKKY exchange interactions between nearby Mn ions
stabilize the observed magnetic order, dominated by and
ordering vectors. These results give compelling evidence that
F-doped LaFeAsO is a strongly correlated electron system at the verge of an
electronic instability.Comment: 5 pages, 5 figures and 4 pages of supplemental materia
Equivalence principle in the new general relativity
We study the problem of whether the active gravitational mass of an isolated
system is equal to the total energy in the tetrad theory of gravitation. The
superpotential is derived using the gravitational Lagrangian which is invariant
under parity operation, and applied to an exact spherically symmetric solution.
Its associated energy is found equal to the gravitational mass. The field
equation in vacuum is also solved at far distances under the assumption of
spherical symmetry. Using the most general expression for parallel vector
fields with spherical symmetry, we find that the equality between the
gravitational mass and the energy is always true if the parameters of the
theory , and satisfy the condition, . In the two special cases where either or
is vanishing, however, this equality is not satisfied for the
solutions when some components of the parallel vector fields tend to zero as
for large .Comment: 18 pages, LaTeX, published in Prog. Theor. Phys. 96 No.5 (1996
- …