1,267 research outputs found
Phase Diagram of -(BEDT-TTF)ICl under High Pressure Based on the First-Principles Electronic Structure
We present a theoretical study on the superconductivity of
-(BEDT-TTF)ICl at 14.2 K under a high hydrostatic
pressure recently found, which is the highest among organic superconductors. In
the present work, we study an effective model using the fluctuation-exchange
(FLEX) approximation based on the results of first-principles calculation. In
the obtained phase diagram, the superconductivity with -like symmetry
is realized next to the antiferromagnetic phase, as a result of the
one-dimensional to two-dimensional crossover driven by the pressure.Comment: 4 pages, 3 figures. accepted for publication in J. Phys. Soc. Jpn.
errors correcte
Positronium signature in organic liquid scintillators for neutrino experiments
Electron anti-neutrinos are commonly detected in liquid scintillator
experiments via inverse beta decay, by looking at the coincidence between the
reaction products, neutron and positron. Prior to positron annihilation, an
electron-positron pair may form an orthopositronium (o-Ps) state, with a mean
life of a few ns. Even if the o-Ps decay is speeded up by spin flip or pick off
effects, it may introduce distortions in the photon emission time distribution,
crucial for position reconstruction and pulse shape discrimination algorithms
in anti-neutrino experiments. Reversing the problem, the o-Ps induced time
distortion represents a new signature for tagging anti-neutrinos in liquid
scintillator.
In this paper, we report the results of measurements of the o-Ps formation
probability and lifetime, for the most used solvents for organic liquid
scintillators in neutrino physics (pseudocumene, linear alkyl benzene,
phenylxylylethane, and dodecane). We characterize also a mixture of
pseudocumene +1.5 g/l of 2,5-diphenyloxazole, a fluor acting as wavelength
shifter.
In the second part of the paper, we demonstrate that the o-Ps induced
distortion of the scintillation photon emission time distributions represent an
optimal signature for tagging positrons on an event by event basis, potentially
enhancing the anti-neutrino detection.Comment: 6 pages, 9 figure
Enhanced Polarized Emission from the One-Parsec-Scale Hotspot of 3C 84 as a Result of the Interaction with Clumpy Ambient Medium
We present Very Long Baseline Array polarimetric observations of the
innermost jet of 3C84 (NGC1275) at 43GHz. A significant
polarized emission is detected at the hotspot of the innermost re-started jet,
which is located 1 pc south from the radio core. While the previous
report presented a hotspot at the southern end of the western limb, the hotspot
location has been moved to the southern end of the eastern limb. Faraday
rotation is detected within an entire bandwidth of the 43-GHz band. The
measured rotation measure (RM) is at most
(6.31.9)radm and might be slightly time
variable on the timescale of a month by a factor of a few. Our measured RM and
the RM previously reported by the CARMA and SMA observations cannot be
consistently explained by the spherical accretion flow with a power-law
profile. We propose that a clumpy/inhomogeneous ambient medium is responsible
for the observed rotation measure. Using equipartition magnetic field, we
derive the electron density of cm. Such an electron
density is consistent with the cloud of narrow line emission region around the
central engine. We also discuss the magnetic field configuration from black
hole scale to pc scale and the origin of low polarization.Comment: 8 pages, 8 figures, accepted for publication in Ap
Gossamer Superconductivity near Antiferromagnetic Mott Insulator in Layered Organic Conductors
Layered organic superconductors are on the verge of the Mott insulator. We
use Gutzwiller variational method to study a Hubbard model including a spin
exchange coupling term. The ground state is found to be a Gossamer
superconductor at small on-site Coulomb repulsion U and an antiferromagnetic
Mott insulator at large U, separated by a first order phase transition. Our
theory is qualitatively consistent with major experiments reported in organic
superconductors.Comment: 5 pages, 3 figure
A quest for frustration driven distortion in Y2Mo2O7
We investigated the nature of the freezing in the geometrically frustrated
Heisenberg spin-glass Y2Mo2O7 by measuring the temperature dependence of the
static internal magnetic field distribution above the spin-glass temperature,
Tg, using the muSR technique. The evolution of the field distribution cannot be
explained by changes in the spin susceptibility alone and suggests a lattice
deformation. This possibility is addressed by numerical simulations of the
Heisenberg Hamiltonian with magneto-elastic coupling at T>0.Comment: 5 pages 4 figures. Accepted for publication in PR
Electronic Scanning in Acoustic Microscopy
Scanning acoustic microscopy (SAM) employs mechanical scanning in both x and y directions. There is one great advantage in this configuration which is that imaging is done on axis, resulting in diffraction limited resolution. However a mechanical system is inherently slow and cumbersome, even though recent advances have brought the scanning time for an image at high frequencies down to the order of a second. For the inspection of inexpensive items such as integrated circuit chips, which is done at frequencies below 100 MHz, it is imperative to have a cheap and ideally real time system. The present work describes recent developments in our laboratory in this directio
Large Kinetic Power in FRII Radio Jets
We investigate the total kinetic powers (L_{j}) and ages (t_{age}) of
powerful jets of four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C
219) by the detail comparison of the dynamical model of expanding cocoons with
observed ones. It is found that these sources have quite large kinetic powers
with the ratio of L_{j} to the Eddington luminosity (L_{Edd}) resides in . Reflecting the large kinetic powers, we also find that the
total energy stored in the cocoon (E_{c}) exceed the energy derived from the
minimum energy condition (E_{min}): . This implies that
a large amount of kinetic power is carried by invisible components such as
thermal leptons (electron and positron) and/or protons.Comment: 5 pages, accepted for publication in Astrophysics and Space Scienc
Magnetic-Field-Induced Antiferromagnetism in Two-Dimensional Hubbard Model: Analysis of CeRhIn
We propose the mechanism for the magnetic-field-induced antiferromagnetic
(AFM) state in a two-dimensional Hubbard model in the vicinity of the AFM
quantum critical point (QCP), using the fluctuation-exchange (FLEX)
approximation by taking the Zeeman energy due to the magnetic field into
account. In the vicinity of the QCP, we find that the AFM correlation
perpendicular to is enhanced, whereas that parallel to is reduced. This
fact means that the finite magnetic field increases , with the AFM order
perpendicular to . The increment in can be understood in terms of the
reduction of both quantum and thermal fluctuations due to the magnetic field,
which is caused by the self-energy effect within the FLEX approximation. The
present study naturally explains the increment in in CeRhIn_5 under the
magnetic field found recently.Comment: 5 page
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
Possible Verification of Tilted Anisotropic Dirac Cone in \alpha-(BEDT-TTF)_2 I_3 Using Interlayer Magnetoresistance
It is proposed that the presence of a tilted and anisotropic Dirac cone can
be verified using the interlayer magnetoresistance in the layered Dirac fermion
system, which is realized in quasi-two-dimensional organic compound
\alpha-(BEDT-TTF)_2 I_3. Theoretical formula is derived using the analytic
Landau level wave functions and assuming local tunneling of electrons. It is
shown that the resistivity takes the maximum in the direction of the tilt if
anisotropy of the Fermi velocity of the Dirac cone is small. The procedure is
described to determine the parameters of the tilt and anisotropy.Comment: 4 pages, 4 figures, corrected Fig.
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