457 research outputs found
Near-infrared mapping of spiral barred galaxies
In external galaxies, near-infrared emission originates from stellar populations, hot dust, free-free emission from H+ regions, gaseous emission, non-thermal nucleus if any. Because of the low extinction compared to the visible, infrared wavelengths are useful to probe regions obscured by dust such as central parts where starburst phenomena can occur because of the large quantity of matter. The results presented were obtained with a 32 x 32 InSb charge injection device (CID) array cooled at 4K, at the f/36 cassegrain focus of the 3m60 Canada-France-Hawaii telescope with a spatial resolution of 0.5 inches per pixel. The objects presented are spiral barred galaxies mapped at J(1.25 microns), H(1.65 microns) and K(2.2 microns). The non-axisymetric potential due to the presence of a bar induces dynamical processes leading to the confinement of matter and peculiar morphologies. Infrared imaging is used to study the link between various components. Correlations with other wavelengths ranges and 2-colors diagrams ((J-H), (H-K)) lead to the identification of star forming regions, nucleus. Maps show structures connected to the central core. The question is, are they flowing away or toward the nucleus. Observations of M83 lead to several conclusions. The star forming region, detected in the visible and the infrared cannot be very compact and must extend to the edge of the matter concentration. The general shape of the near-infrared emission and the location of radio and 10 micron peaks suggest the confinement of matter between the inner Linblad resonances localized from CO measurements about 100 and 400 pc. The distribution of color indices in the arc from southern part to the star forming region suggests an increasing amount of gas and a time evolution eventually triggered by supernova explosions. Close to the direction of the bar, a bridge-like structure connects the arc to the nucleus with peculiar color indices. Perhaps, this structure can be linked to a height velocity component seen in UV and we can attribute it to a jet and/or a matter flow along the bar toward the nucleus, fuelling it. NGC 1068 is the nearest Seyfert 2 galaxy. It has been a subject of many studies at all wavelengths. This object was mapped at J, H, K, L and M, and in polaro-imagery. Results are given
Evidence for two distinct energy scales in the Raman spectra of YBa2(CuNi)O6.95
We report low energy electronic Raman scattering from Ni-substituted
YBa2Cu3O6.95 single crystals with Tc ranging from 92.5 K to 78 K. The fully
symmetrical A1g channel and the B1g channel which is sensitive to the dx2-y2
gap maximum have been explored. The energy of the B1g pair-breaking peak
remains constant under Ni doping while the energy of the A1g peak scales with
Tc (EA1g/Tc=5). Our data show that the A1g peak tracks the magnetic resonance
peak observed in inelastic neutron scattering yielding a key explanation to the
long-standing problem of the origin the A1g peak.Comment: 10 pages, 4 figures and 1 tabl
Temperature dependence and resonance effects in Raman scattering of phonons in NdFeAsOF single crystals
We report plane-polarized Raman scattering spectra of iron oxypnictide
superconductor NdFeAsOF single crystals with varying fluorine
content. The spectra exhibit sharp and symmetrical phonon lines with a weak
dependence on fluorine doping . The temperature dependence does not show any
phonon anomaly at the superconducting transition. The Fe related phonon
intensity shows a strong resonant enhancement below 2 eV. We associate the
resonant enhancement to the presence of an interband transition around 2 eV
observed in optical conductivity. Our results point to a rather weak coupling
between Raman-active phonons and electronic excitations in iron oxypnictides
superconductors.Comment: 4 pages, 3 figures, to appear in Phys. Rev.
Coupling between quasiparticles and a bosonic mode in the normal state of HgBaCuO
We report a doping dependent study of the quasiparticles dynamics in
HgBaCuO via Electronic Raman Scattering. A well-defined energy
scale is found in the normal state dynamics of the quasiparticles over a broad
doping range. It is interpreted as evidence for coupling between the
quasiparticles and a collective bosonic mode whose energy scale depend only
weakly with doping. We contrast this behavior with that of the superconducting
gap whose amplitude near the node continuously decreases towards the underdoped
regime. We discuss the implications of our findings on the nature of the
collective mode and argue that electron-phonon coupling is the most natural
explanation.Comment: 5 pages, 4 figure
Electromagnon and phonon excitations in multiferroic TbMnO3
We have performed Raman measurements on TbMnO3 single crystal under magnetic
field along the three crystallographic directions. The flip of the spin spiral
plane creates an electromagnon excitation. In addition to the electromagnons
induced by the Heisenberg coupling, we have detected the electromagnon created
by the Dzyaloshinskii-Moriya interaction along the c axis. We have identified
all the vibrational modes of TbMnO3. Their temperature dependences show that
only one phonon observed along the polarization axis is sensitive to the
ferroelectric transition. This mode is tied to the Tb3+ ion displacements that
contribute to the ferroelectric polarization
Amplitude `Higgs' mode in 2H-NbSe2 Superconductor
We report experimental evidences for the observation of the superconducting
amplitude mode, so-called `Higgs' mode in the charge density wave
superconductor 2H-NbSe2 using Raman scattering. By comparing 2H-NbSe2 and its
iso-structural partner 2H-NbS2 which shows superconductivity but lacks the
charge density wave order, we demonstrate that the superconducting mode in
2H-NbSe2 owes its spectral weight to the presence of the coexisting charge
density wave order. In addition, temperature dependent measurements in 2H-NbSe2
show a full spectral weight transfer from the charge density wave mode to the
superconducting mode upon entering the superconducting phase. Both observations
are fully consistent with a superconducting amplitude mode or Higgs mode.Comment: Accepted for publication in Phys. Rev. B Rapid Com. 5 pages with 3
figure
Magneto-electric excitations in multiferroic TbMnO3 by Raman scattering
Low energy excitations in the multiferroic material TbMnO3 have been
investigated by Raman spectroscopy. Our observations reveal the existence of
two peaks at 30 cm-1 and 60 cm-1. They are observed in the cycloidal phase
below the Curie temperature but not in the sinusoidal phase, suggesting their
magnetoelectric origin. While the peak energies coincide with the frequencies
of electromagnons measured previously by transmission spectroscopy, they show
surprisingly different selection rules, with the 30 cm-1 excitation enhanced by
the electric field of light along the spontaneous polarization. The origins of
the modes are discussed under Raman and infrared selection rules
considerations
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