1,872 research outputs found
Origin of the anomalous magnetic circular dichroism spectral shape in ferromagnetic (Ga,Mn)As: Impurity bands inside the band gap
The electronic structure of a prototype dilute magnetic semiconductor (DMS),
Ga1-xMnxAs, is studied by magnetic circular dichroism (MCD) spectroscopy. We
prove that the optical transitions originated from impurity bands cause the
strong positive MCD background. The MCD signal due to the E0 transition from
the valence band to the conduction band is negative indicating that the p-d
exchange interactions between the p-carriers and d-spin is antiferromagnetic.
The negative E0 MCD signal also indicates that the hole-doping of the valence
band is not so large as previously assumed. The impurity bands seem to play
important roles for the ferromagnetism of Ga1-xMnxAs.Comment: 13 pages, 3 figure
QPO Evolution in 2005 Outburst of the Galactic Nano Quasar GRO J1655-40
GRO J1655-40 showed significant X-ray activity in the last week of February,
2005 and remained active for the next 260 days. The rising and the decline
phases of this particular outburst show evidence for systematic movements of
the Comptonizing region, assumed to be a CENBOL, which causes the
Quasi-periodic Oscillations or QPOs. We present both the spectral and the
timing results of the RXTE/PCA data taken from these two hard spectral states.
Assuming that the QPOs originate from an oscillating shock CENBOL, we show how
the shock slowly moves in through the accretion flow during the rising phase at
a constant velocity and accelerate away outward during the later part of the
decline phase. By fitting the observed frequencies with our solution, we
extract time variation of various disk parameters such as the shock locations,
velocity etc.Comment: 5 Pages, 2 Figures, Proceeding of the 2nd Kolkata Conference on
"Observational Evidence for the Black Holes in the Universe", Published in
AIP, 200
Shell Crossing Singularities in Quasi-Spherical Szekeres Models
We investigate the occurrence of shell crossing singularities in
quasi-spherical Szekeres dust models with or without a cosmological constant.
We study the conditions for shell crossing singularity both from physical and
geometrical point of view and they are in agreement.Comment: 10 latex pages, RevTex style, no figure
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