900 research outputs found
Field-induced staggered magnetic moment in the quasi-two-dimensional organic Mott insulator -(BEDT-TTF)Cu[N(CN)]Cl
We investigated the magnetism under a magnetic field in the
quasi-two-dimensional organic Mott insulator
-(BEDT-TTF)Cu[N(CN)]Cl through magnetization and
C-NMR measurements. We found that in the nominally paramagnetic phase
(i.e., above N\'eel temperature) the field-induced local moments have a
staggered component perpendicular to the applied field. As a result, the
antiferromagnetic transition well defined at a zero field becomes crossover
under a finite field. This unconventional behavior is qualitatively reproduced
by the molecular-field calculation for Hamiltonian including the exchange,
Dzyaloshinsky-Moriya (DM), and Zeeman interactions. This calculation also
explains other unconventional magnetic features in
-(BEDT-TTF)Cu[N(CN)]Cl reported in the literature. The
present results highlight the importance of the DM interaction in field-induced
magnetism in a nominally paramagnetic phase, especially in low-dimensional spin
systems.Comment: 11 pages, 12 figures, selected for Editors' Suggestion
NMR evidence for very slow carrier density fluctuations in the organic metal (TMTSF)ClO
We have investigated the origin of the large increase in spin-echo decay
rates for the Se nuclear spins at temperatures near to in the
organic superconductor (TMTSF)ClO. The measured angular dependence of
demonstrates that the source of the spin-echo decays lies with
carrier density fluctuations rather than fluctuations in TMTSF molecular
orientation. The very long time scales are directly associated with the
dynamics of the anion ordering occurring at , and the inhomogeneously
broadened spectra at lower temperatures result from finite domain sizes. Our
results are similar to observations of line-broadening effects associated with
charge-ordering transitions in quasi-two dimensional organic conductors.Comment: 5 pages, 4 figure
Mott Transition from a Spin Liquid to a Fermi Liquid in the Spin-Frustrated Organic Conductor kappa-(ET)2Cu2(CN)3
Pressure-temperature phase diagram of the organic Mott insulator
-(ET)Cu(CN), a model system of the spin liquid on
triangular lattice, has been investigated by H NMR and resistivity
measurements. The spin-liquid phase is persistent before the Mott transition to
the metal or superconducting phase under pressure. At the Mott transition, the
spin fluctuations are rapidly suppressed and the Fermi-liquid features are
observed in the temperature dependence of the spin-lattice relaxation rate and
resistivity. The characteristic curvature of Mott boundary in the phase diagram
highlights a crucial effect of the spin frustration on the Mott transition.Comment: 4 pages, 5 figure
Telerobotics test bed for space structure assembly
A cooperative research on super long distance space telerobotics is now in progress both in Japan and USA. In this program. several key features will be tested, which can be applicable to the control of space robots as well as to terrestrial robots. Local (control) and remote (work) sites will be shared between Electrotechnical Lab (ETL) of MITI in Japan and Jet Propulsion Lab (JPL) in USA. The details of a test bed for this international program are discussed in this report
Wet and dry deposition of mineral dust particles in Japan: factors related to temporal variation and spatial distribution
Recent ground networks and satellite remote-sensing observations have
provided useful data related to spatial and vertical distributions of
mineral dust particles in the atmosphere. However, measurements of temporal
variations and spatial distributions of mineral dust deposition fluxes are
limited in terms of their duration, location, and processes of deposition.
To ascertain temporal variations and spatial distributions of mineral dust
deposition using wet and dry processes, weekly deposition samples were
obtained at Sapporo, Toyama, Nagoya, Tottori, Fukuoka, and Cape Hedo
(Okinawa) in Japan during October 2008–December 2010 using automatic wet
and dry separating samplers. Mineral dust weights in water-insoluble residue
were estimated from Fe contents measured using an X-ray fluorescence
analyser. Wet and dry deposition fluxes of mineral dusts were both high in
spring and low in summer, showing similar seasonal variations to frequency
of aeolian dust events (Kosa) in Japan. For wet deposition, highest and lowest
annual dust fluxes were found at Toyama (9.6 g m<sup>−2</sup> yr<sup>−1</sup>) and at
Cape Hedo (1.7 g m<sup>−2</sup> yr<sup>−1</sup>) as average values in 2009 and 2010.
Higher wet deposition fluxes were observed at Toyama and Tottori, where
frequent precipitation (> 60% days per month) was observed
during dusty seasons. For dry deposition among Toyama, Tottori, Fukuoka, and
Cape Hedo, the highest and lowest annual dust fluxes were found respectively
at Fukuoka (5.2 g m<sup>−2</sup> yr<sup>−1</sup>) and at
Cape Hedo (2.0 g m<sup>−2</sup> yr<sup>−1</sup>)
as average values in 2009 and 2010. The average ratio of wet and
dry deposition fluxes was the highest at Toyama (3.3) and the lowest at Hedo
(0.82), showing a larger contribution of the dry process at western sites,
probably because of the distance from desert source regions and because of
the effectiveness of the wet process in the dusty season.
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Size distributions of refractory dust particles were obtained using
four-stage filtration: > 20, > 10, > 5, and > 1 μm diameter. Weight fractions of the sum of
> 20 μm and 10–20 μm (giant fraction) were
higher than 50% for most of the event samples. Irrespective of the
deposition type, the giant dust fractions generally decreased with increasing
distance from the source area, suggesting the selective depletion of larger
giant particles during atmospheric transport. Based on temporal variations of
PM<sub>c</sub> (2.5 < <i>D</i> < 10 μm),
ground-based lidar, backward air trajectories, and vertical profiles of
potential temperatures, transport processes of dust particles are discussed
for events with high-deposition and low-deposition flux with high
PM<sub>c</sub>. Low dry dust depositions with high PM<sub>c</sub>
concentrations were observed under stronger (5 K km<sup>−1</sup>) stratification
of potential temperature with thinner and lower (< 2 km)
dust distributions because the PM<sub>c</sub> fraction of dust particles
only survived after depletion of giant dust particles by rapid gravitational
settling at the time they reach Japan. In contrast, transport through a
thicker (> 2 km) dust layer with weak vertical gradient of
potential temperature carry more giant dust particles to Japan. Because giant
dust particles are an important mass fraction of dust accumulation,
especially in the North Pacific, which is known as a high-nutrient,
low-chlorophyll (HNLC) region, the transport height and fraction of giant
dust particles are important factors for studying dust budgets in the
atmosphere and their role in biogeochemical cycles
Absence of a Spin Liquid Phase in the Hubbard Model on the Honeycomb Lattice
A spin liquid is a novel quantum state of matter with no conventional order
parameter where a finite charge gap exists even though the band theory would
predict metallic behavior. Finding a stable spin liquid in two or higher
spatial dimensions is one of the most challenging and debated issues in
condensed matter physics. Very recently, it has been reported that a model of
graphene, i.e., the Hubbard model on the honeycomb lattice, can show a spin
liquid ground state in a wide region of the phase diagram, between a semi-metal
(SM) and an antiferromagnetic insulator (AFMI). Here, by performing numerically
exact quantum Monte Carlo simulations, we extend the previous study to much
larger clusters (containing up to 2592 sites), and find, if any, a very weak
evidence of this spin liquid region. Instead, our calculations strongly
indicate a direct and continuous quantum phase transition between SM and AFMI.Comment: 15 pages with 7 figures and 9 tables including supplementary
information, accepted for publication in Scientific Report
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