40,600 research outputs found
On the Origin of the Non-Fermi Liquid Behavior of SrRuO_{3}
Motivated by the unusual features observed in the transport properties of the
ferromagnetic "bad metal" , we construct a model incorporating
essential features of the realistic structure of this nearly cubic material. In
particular, we show how the orbital {\it orientation} in the perfectly
cubic structure determines the peculiar structure of the hybridization matrix,
and demonstrate how the local non-Fermi liquid features arise when interactions
are switched on. we discuss the effect of the slight deviation from the cubic
structure (at low-) qualitatively. The model provides a consistent
explanation of the features observed recently in the optical response of
.Comment: 4 pages. Submitted to Physical Review Letter
Rotating massive O stars with non-spherical 2D winds
We present solutions for the velocity field and mass-loss rates for 2D
axisymmetric outflows, as well as for the case of mass accretion through the
use of the Lambert W-function. For the case of a rotating radiation-driven wind
the velocity field is obtained analytically using a parameterised description
of the line acceleration that only depends on radius r at any given latitude
. The line acceleration g(r) is obtained from Monte-Carlo multi-line
radiative transfer calculations. The critical/sonic point of our equation of
motion varies with latitude . Furthermore, an approximate analytical
solution for the supersonic flow of a rotating wind is derived, which is found
to closely resemble the exact solution. For the simultaneous solution of the
mass-loss rate and velocity field, we use the iterative method of our 1D method
extended to the non-spherical 2D case. We apply the new theoretical expressions
with our iterative method to the stellar wind from a differentially rotating 40
O5-V main sequence star as well as to a 60 O-giant star,
and we compare our results to previous studies that are extensions of the
Castor et al. (1975, ApJ, 195, 157) CAK formalism. Next, we account for the
effects of oblateness and gravity darkening. Our numerical results predict an
equatorial decrease of the mass-loss rate, which would imply that
(surface-averaged) total mass-loss rates are lower than for the spherical 1D
case, in contradiction to the Maeder & Meynet (2000, A&A, 361, 159) formalism
that is oftentimes employed in stellar evolution calculations for rotating
massive stars. To clarify the situation in nature we discuss observational
tests to constrain the shapes of large-scale 2D stellar winds.Comment: 20 pages, 4 figures, 7 tables, accepted for publication in A&A, (one
corrected sentence in sect. 4.1.), a generalization of arXiv paper:
arXiv:0810.190
Orbital Switching and the First-Order Insulator-Metal Transition in Paramagnetic V_2O_3
The first-order metal-insulator transition (MIT) in paramagnetic
is studied within the ab-initio scheme LDA+DMFT, which merges the local density
approximation (LDA) with dynamical mean field theory (DMFT). With a fixed value
of the Coulomb , we show how the abrupt pressure driven MIT is
understood in a new picture: pressure-induced decrease of the trigonal
distortion within the strong correlation scenario (which is not obtained within
LDA). We find good quantitative agreement with switch of the orbital
occupation of and the spin state S=1
across the MIT, thermodynamics and resistivity, and the
one-electron spectral function, within this new scenario.Comment: 4 pages, 4 figures, submitted to PR
Insulator-Metal transition in the Doped 3d1 Transition Metal Oxide LaTiO3
The doping induced insulator-metal transition in is
studied using the ab-initio LDA+DMFT method. Combining the LDA bandstructure
for the actual, distorted structure found recently with multi-orbital DMFT to
treat electronic correlations, we find: ferro-orbital order in the Mott
insulating state without orbital degeneracy, a continuous filling
induced transition to the paramagnetic metal (PM) with , and
excellent quantitative agreement with published photoemission data for the case
of 6% doping. Our results imply that this system can be described as a
Mott-Hubbard system without orbital (liquid) degeneracy.Comment: 4 pages, 3 figures, submitted to PR
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