1,521 research outputs found
Phonon, Two-Magnon and Electronic Raman Scattering of Fe1+yTe1-xSex
We have measured Raman scattering spectra of single-crystalline FeTe0.6Se0.4
(T_c ~ 14.5 K) and its parent compound Fe1.074Te at various temperatures. In
the parent compound Fe1.074Te, A1g and B1g modes have been observed at 157.5
and 202.3 cm-1, respectively, at 5 K. These frequencies qualitatively agree
with the calculated results. Two-magnon excitation has been observed around
2300 cm-1 for both compounds. Temperature dependence between the electronic
Raman spectra below and above T_c has been observed and 2\Delta and
2\Delta/k_BT_C have been estimated as 5.0 meV and 4.0, respectively.Comment: 8 pages, 8 figures, to be published in Phys. Rev.
Galactic Wind in the Nearby Starburst Galaxy NGC 253 Observed with the Kyoto3DII Fabry-Perot Mode
We have observed the central region of the nearby starburst galaxy NGC 253
with the Kyoto Tridimensional Spectrograph II (Kyoto3DII) Fabry-Perot mode in
order to investigate the properties of its galactic wind. Since this galaxy has
a large inclination, it is easy to observe its galactic wind. We produced the
Ha, [N II]6583, and [S II]6716,6731 images, as well as those line ratio maps.
The [N II]/Ha ratio in the galactic wind region is larger than those in H II
regions in the galactic disk. The [N II]/Ha ratio in the southeastern filament,
a part of the galactic wind, is the largest and reaches about 1.5. These large
[N II]/Ha ratios are explained by shock ionization/excitation. Using the [S
II]/Ha ratio map, we spatially separate the galactic wind region from the
starburst region. The kinetic energy of the galactic wind can be sufficiently
supplied by supernovae in a starburst region in the galactic center. The shape
of the galactic wind and the line ratio maps are non-axisymmetric about the
galactic minor axis, which is also seen in M82. In the [N II]6583/[S
II]6716,6731 map, the positions with large ratios coincide with the positions
of star clusters found in the Hubble Space Telescope (HST) observation. This
means that intense star formation causes strong nitrogen enrichment in these
regions. Our unique data of the line ratio maps including [S II] lines have
demonstrated their effectiveness for clearly distinguishing between shocked gas
regions and starburst regions, determining the extent of galactic wind and its
mass and kinetic energy, and discovering regions with enhanced nitrogen
abundance.Comment: 22 pages, 5 figures, 1 table, accepted for publication in Ap
Electron Correlation Driven Heavy-Fermion Formation in LiV2O4
Optical reflectivity measurements were performed on a single crystal of the
d-electron heavy-fermion (HF) metal LiV2O4. The results evidence the highly
incoherent character of the charge dynamics for all temperatures above T^*
\approx 20 K. The spectral weight of the optical conductivity is redistributed
over extremely broad energy scales (~ 5 eV) as the quantum coherence of the
charge carriers is recovered. This wide redistribution is, in sharp contrast to
f-electron Kondo lattice HF systems, characteristic of a metallic system close
to a correlation driven insulating state. Our results thus reveal that strong
electronic correlation effects dominate the low-energy charge dynamics and
heavy quasiparticle formation in LiV2O4. We propose the geometrical
frustration, which limits the extension of charge and spin ordering, as an
additional key ingredient of the low-temperature heavy-fermion formation in
this system.Comment: 5 pages, 3 figure
High-Energy Spin Dynamics in LaSrNiO
We have mapped out the spin dynamics in a stripe-ordered nickelate,
LaSrNiO with , using inelastic neutron
scattering. We observe spin-wave excitations up to 80 meV emerging from the
incommensurate magnetic peaks with an almost isotropic spin-velocity: eV \AA, very similar to the velocity in the undoped, insulating
parent compound, LaNiO. We also discuss the similarities and
differences of the inferred spin-excitation spectrum with those reported in
superconducting high- cuprates.Comment: 4 figure
Role of electron-electron and electron-phonon interaction effect in the optical conductivity of VO2
We have investigated the charge dynamics of VO2 by optical reflectivity
measurements. Optical conductivity clearly shows a metal-insulator transition.
In the metallic phase, a broad Drude-like structure is observed. On the other
hand, in the insulating phase, a broad peak structure around 1.3 eV is
observed. It is found that this broad structure observed in the insulating
phase shows a temperature dependence. We attribute this to the electron-phonon
interaction as in the photoemission spectra.Comment: 6 pages, 8 figures, accepted for publication in Phys. Rev.
Charging and trapping of macroparticles in near-electrode regions of fluorocarbon plasmas with negative ions
Charging and trapping of macroparticles in the near-electrode region of fluorocarbon etching plasmas with negative ions is considered. The equilibrium charge and forces on particles are computed as a function of the local position in the plasma presheath and sheath. The ionic composition of the plasma corresponds to the etching experiments in 2.45 GHz surface-wave sustained and 13.56 MHz inductively coupled C4F8+Ar plasmas. It is shown that despite negligible negative ion currents collected by the particles, the negative fluorine ions affect the charging and trapping of particulates through modification of the sheath/presheath structure
- …