32,130 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
Prebiotic Organic Microstructures
Micro- and sub-micrometer spheres, tubules and fiber-filament soft structures have been synthesized in our experiments conducted with 3 MeV proton irradiations of a mixture of simple inorganic constituents, CO, N2 and H2O. We analysed the irradiation products, with scanning electron microscopy (SEM) and atomic force microscopy (AFM). These laboratory organic structures produced wide variety of proteinous and non-proteinous amino acids after HCl hydrolysis. The enantiomer analysis for D-, L- alanine confirmed that the amino acids were abiotically synthesized during the laboratory experiment. Considering hydrothermal activity, the presence of CO2 and H2, of a ferromagnesian silicate mineral environment, of an Earth magnetic field which was much less intense during Archean times than nowadays and consequently of a proton excitation source which was much more abundant, we propose that our laboratory organic microstructures might be synthesized during Archean times. We show similarities in morphology and in formation with some terrestrial Archean microstructures and we suggest that some of the observed Archean carbon spherical and filamentous microstructures might be composed of abiogenic organic molecules. We further propose a search for such prebiotic organic signatures on Mars. This article has been posted on Nature precedings on 21 July 2010 [1]. Extinct radionuclides as source of excitation have been replaced by cosmic radiations which were much more intense 3.5 Ga ago because of a much less intense Earth magnetic field. The new version of the article has been presented at the ORIGINS conference in Montpellier in july 2011 [2] and has since been published in Origins of Life and Evolution of Biospheres 42 (4) 307-316, 2012. 
DOI: 10.1007/s11084-012-9290-5 


Current-feedback-stabilized laser system for quantum simulation experiments using Yb clock transition at 578 nm
We developed a laser system for the spectroscopy of the clock transition in
ytterbium (Yb) atoms at 578 nm based on an interference-filter stabilized
external-cavity diode laser (IFDL) emitting at 1156 nm. Owing to the improved
frequency-to-current response of the laser-diode chip and the less sensitivity
of the IFDL to mechanical perturbations, we succeeded in stabilizing the
frequency to a high-finesse ultra-low-expansion glass cavity with a simple
current feedback system. Using this laser system, we performed high-resolution
clock spectroscopy of Yb and found that the linewidth of the stabilized laser
was less than 320 Hz.Comment: 5 pages, 7 figure
Origin of the Weak Pseudo-gap Behaviors in Na_{0.35}CoO_2: Absence of Small Hole Pockets
We analyze the ``normal electronic states'' of Na_{0.35}CoO_2 based on the
effective d-p model with full d-orbital freedom using the fluctuation-exchange
(FLEX) approximation. They sensitively depend on the topology of the Fermi
surfaces, which changes as the crystalline electric splitting (CES) due to the
trigonal deformation. We succeed in reproducing the weak pseudo-gap behaviors
in the density of states (DOS) and in the uniform magnetic susceptibility below
300K, assuming that six small hole-pockets predicted by LDA band calculations
are absent. When they exist, on the contrary, then ``anti-pseudo-gap
behaviors'' should inevitably appear. Thus, the present study strongly supports
the absence of the small hole-pockets in Na_{0.35}CoO_2, as reported by recent
ARPES measurements. A large Fermi surface around the \Gamma-point would account
for the superconductivity in water-intercalated samples.Comment: 5pages, to appear in J. Phys. Soc. Jpn. Vol.74 (2005) No.
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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