1,399 research outputs found
Core-Level X-Ray Photoemission Satellites in Ruthenates: A New Mechanism Revealing the Mott Transition
Ru 3d core-level x-ray photoemission spectra of various ruthenates are
examined. They show in general two-peak structures, which can be assigned as
the screened and unscreened peaks. The screened peak is absent in a Mott
insulator, but develops into a main peak in the metallic regime. This spectral
behavior is well explained by the dynamical mean-field theory calculation for
the single-band Hubbard model with on-site core-hole potential using the exact
diagonalization method. The new mechanism of the core-level photoemission
satellite can be utilized to reveal the Mott transition phenomenon in various
strongly correlated electron systems, especially in nano-scale devices and
phase-separated materials.Comment: 4 pages, 5 figures, submitted to PR
Studies on multiplication effect of noises of PPDs, and a proposal of a new structure to improve the performance
Pixelated Photon Detectors (PPDs) are the most promising semiconductor
photodetectors in recent years. One of the issues with the PPD is its high
noise rate. As well as random noise, PPD also exhibits so called after-pulsing
and optical crosstalk, and these limit the applicable range of its gain as well
as its size. By accurately measuring each of these causes of noises
independently, we quantitatively evaluated how the performance of the present
device is limited by multiplication effect of these noises. With this result
and the pulsing mechanism of PPD, we propose a new structure of PPD which could
have high gain with low noise.Comment: Submitted to Nuclear Instruments and Methods in Physics Research,
Anomalous geomagnetic variations associated with the volcanic activity of the Mayon volcano, Philippines during 2009–2010
AbstractLocal anomalous geomagnetic variations preceding and accompanying the volcanic eruptions had been reported by several researchers. This paper uses continuous high-resolution geomagnetic data to examine the occurrence of any anomalous geomagnetic field variations that possibly linked with the volcanic eruption of the Mayon volcano, Philippines during 2009–2010. The nearest geomagnetic observing point from the Mayon volcano is the Legazpi (LGZ) station, Philippines; which is located about 13km South of the Mayon volcano. The amplitude range of daily variations and the amplitude of Ultra Low Frequency emissions in the Pc3 range (Pc3; 10–45s) were examined at the LGZ station and also were compared with those from the Davao (DAV) station, Philippines as a remote reference station. Both the LGZ and DAV stations belong to the MAGDAS Network. The result of data analysis reveals significant anomalous changes in the amplitude range of daily variations and the Pc3 amplitude at the LGZ station before and during the volcanic eruption of the Mayon volcano. From the obtained results, it appears that the observed anomalous variations are dependent on the change in the underground conductivity connected with variation in the physical properties of the Earth’s crust due to the activity of the Mayon volcano. Therefore, these anomalous geomagnetic variations are considered to be of a local volcanic origin
1s2p resonant inelastic x-ray scattering in a-Fe2O3
We report experimental and theoretical results on the Fe K edge x-ray absorption spectrum and 1s2p
resonant inelastic x-ray scattering (RIXS) spectra in a-Fe2O3 . The results are interpreted using an FeO6^9-
cluster model with intra-atomic multiplet coupling and interatomic covalency hybridization. The 1s2p RIXS is
treated as a coherent second-order optical process. It is shown that the double-peak structure in the pre-edge
region of Fe K absorption spectrum is due to the cubic crystal-field splitting, and that the intensity of the
eg (t2g) component in the 1s2p resonant inelastic spectrum is enhanced by tuning the incident photon energy
to the eg (t2g) component in the absorption spectrum
Electronic Structure and Phase Transition in V2O3: Importance of 3d Spin-Orbit Interaction and Lattice Distortion
The 3d electronic structure and phase transition in pure and Cr doped V2O3
are theoretically investigated in relation to the 3d spin-orbit interaction and
lattice distortion. A model consisting of the nearest-neighbor V ion pair with
full degeneracy of the 3d orbitals is studied within the many-body point of
view. It is shown that each V ion with S=1 spin state has a large orbital
magnetic moment and no orbital ordering occurs in the
antiferromagnetic insulating (AFI) phase. The anomalous resonant Bragg
reflection found in the AFI phase is attributed to the magnetic ordering. In
the AFI and paramagnetic insulating (PI) phases, Jahn-Teller like lattice
instability leads to tilting of the V ion pairs from the corundum c-axis and
this causes large difference in the orbital occupation between the paramagnetic
metal and the insulating phases, which is consistent with linear dichroic V 2p
XAS measurements.
To understand the AFI to PI transition, a model spin Hamiltonian is also
proposed. The transition is found to be simultaneous order-disorder transition
of the magnetic moments and tilting directions of the V ion pairs. Softening of
elastic constant C44 and abrupt change in short range spin correlations
observed at the transition are also explained.Comment: 18 pages, 16 figure
Direct Neutron Capture for Magic-Shell Nuclei
In neutron capture for magic--shell nuclei the direct reaction mechanism can
be important and may even dominate. As an example we investigated the reaction
Ca(n,Ca for projectile energies below 250\,keV in a direct
capture model using the folding procedure for optical and bound state
potentials. The obtained theoretical cross sections are in agreement with the
experimental data showing the dominance of the direct reaction mechanism in
this case. The above method was also used to calculate the cross section for
Ca(n,Ca.Comment: REVTeX, 7 pages plus 3 uuencoded figures, the complete uuencoded
postscript file is available at ftp://is1.kph.tuwien.ac.at/pub/ohu/calcium.u
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Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset
Substorm onset is marked in the ionosphere by the sudden brightening of an existing auroral arc or the creation of a new auroral arc. Also present is the formation of auroral beads, proposed to play a key role in the detonation of the substorm, as well as the development of the large-scale substorm current wedge (SCW ), invoked to carry the current diversion. Both these phenomena, auroral beads and the SCW, have been intimately related to ultra-low frequency (ULF) waves of specific frequencies as observed by ground-based magnetometers. We present a case study of the absolute and relative timing of Pi1 and Pi2 ULF wave bands with regard to a small substorm expansion phase onset. We find that there is both a location and frequency dependence for the onset of ULF waves. A clear epicentre is observed in specific wave frequencies concurrent with the brightening of the substorm onset arc and the presence of “auroral beads”. At higher and lower wave frequencies, different epicentre patterns are revealed, which we conclude demonstrate different characteristics of the onset process; at higher frequencies, this epicentre may demonstrate phase mixing, and at intermediate and lower frequencies these epicentres are characteristic of auroral beads and cold plasma approximation of the “Tamao travel time” from near-earth neutral line reconnection and formation of the SCW
Electronic Structure and Valence Band Spectra of Bi4Ti3O12
The x-ray photoelectron valence band spectrum and x-ray emission valence-band
spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented
(analyzed in the common energy scale) and interpreted on the basis of a
band-structure calculation for an idealized I4/mmm structure of this material.Comment: 6 pages + 7 PostScript figures, RevTex3.0, to be published in
Phys.Rev.B52 (Oct.95). Figures also available via anonymous ftp at
ftp://ftp.physik.uni-osnabrueck.de/pub/apostnik/BiTiO
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