17,450 research outputs found
Anomalous infrared spectra of hybridized phonons in type-I clathrate BaGaGe
The optical conductivity spectra of the rattling phonons in the clathrate
BaGaGe are investigated in detail by use of the terahertz
time-domain spectroscopy. The experiment has revealed that the lowest-lying
vibrational mode of a Ba(2) ion consists of a sharp Lorentzian peak at
1.2 THz superimposed on a broad tail weighted in the lower frequency regime
around 1.0 THz. With decreasing temperature, an unexpected linewidth broadening
of the phonon peak is observed, together with monotonic softening of the phonon
peak and the enhancement of the tail structure. These observed anomalies are
discussed in terms of impurity scattering effects on the hybridized phonon
system of rattling and acoustic phonons.Comment: Submitted to JPS
Antiferromagnetic Phases of One-Dimensional Quarter-Filled Organic Conductors
The magnetic structure of antiferromagnetically ordered phases of
quasi-one-dimensional organic conductors is studied theoretically at absolute
zero based on the mean field approximation to the quarter-filled band with
on-site and nearest-neighbor Coulomb interaction. The differences in magnetic
properties between the antiferromagnetic phase of (TMTTF)X and the spin
density wave phase in (TMTSF)X are seen to be due to a varying degrees of
roles played by the on-site Coulomb interaction. The nearest-neighbor Coulomb
interaction introduces charge disproportionation, which has the same spatial
periodicity as the Wigner crystal, accompanied by a modified antiferromagnetic
phase. This is in accordance with the results of experiments on (TMTTF)Br
and (TMTTF)SCN. Moreover, the antiferromagnetic phase of (DI-DCNQI)Ag
is predicted to have a similar antiferromagnetic spin structure.Comment: 8 pages, LaTeX, 4 figures, uses jpsj.sty, to be published in J. Phys.
Soc. Jpn. 66 No. 5 (1997
Charge Ordering in alpha-(BEDT-TTF)2I3 by synchrotron x-ray diffraction
The spatial charge arrangement of a typical quasi-two-dimensional organic
conductor alpha-(BEDT-TTF)2I3 is revealed by single crystal structure analysis
using synchrotron radiation. The results show that the horizontal stripe type
structure, which was suggested by mean field theory, is established. We also
find the charge disproportion above the metal-insulator transition temperature
and a significant change in transfer integrals caused by the phase transition.
Our result elucidates the insulating phase of this material as a 2k_F charge
density localization.Comment: 8 pages, 5 figures, 1 tabl
The 90 GHz radiometric imaging
A 90-GHz (3 mm wavelength) radiometer with a noise output fluctuation of 0.22 K (RMS), with a scanning antenna beam mirror, and the data processing system are described. Real-time radiometric imaging of terrain and man-made objects are shown. Flying at an altitude of 1500 ft a radiometer antenna with a 2 degrees halfpower beamwidth can distinguish landforms, waterways, roads, runways, bridges, ships at sea and their wakes, aircraft on runways, and athletic fields. A flight taken at an altitude of 3000 ft with approximately 2000 ft of clouds below the radiometer demonstrates the ability to distinguish bridges, rivers, marshland and other landforms even though the clouds are optically opaque. The radiometric images of a few representative scenes along with photographs of the corresponding scenes are presented to demonstrate the resolution of the imager system
Charge Ordering in Organic ET Compounds
The charge ordering phenomena in quasi two-dimensional 1/4-filled organic
compounds (ET)_2X (ET=BEDT-TTF) are investigated theoretically for the
and -type structures, based on the Hartree approximation for the
extended Hubbard models with both on-site and intersite Coulomb interactions.
It is found that charge ordered states of stripe-type are stabilized for the
relevant values of Coulomb energies, while the spatial pattern of the stripes
sensitively depends on the anisotropy of the models. By comparing the results
of calculations with the experimental facts, where the effects of quantum
fluctuation is incorporated by mapping the stripe-type charge ordered states to
the S=1/2 Heisenberg Hamiltonians, the actual charge patterns in the insulating
phases of -(ET)_2MM'(SCN)_4 and -(ET)_2I_3 are deduced.
Furthermore, to obtain a unified view among the , and
-(ET)_2X families, the stability of the charge ordered state in
competition with the dimeric antiferromagnetic state viewed as the Mott
insulating state, which is typically realized in -type compounds, and
with the paramagnetic metallic state, is also pursued by extracting essential
parameters.Comment: 35 pages, 27 figures, submitted to J. Phys. Soc. Jp
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