219 research outputs found
Vanadium dioxide : A Peierls-Mott insulator stable against disorder
Vanadium dioxide undergoes a first order metal-insulator transition at 340 K.
In this work, we develop and carry out state of the art linear scaling DFT
calculations refined with non-local dynamical mean-field theory. We identify a
complex mechanism, a Peierls-assisted orbital selection Mott instability, which
is responsible for the insulating M phase, and furthermore survives a
moderate degree of disorder.Comment: 5 pages, 4 figures. Supplementary material 8 pages, 4 figures. This
version (v2) matches that accepted for Physical Review Letters on 16th May
201
Evidence for Multiple Phase Transitions in La_1-xCa_xCoO_3
We report thermal-expansion and specific-heat data of the series
La_1-xCa_xCoO_3 for 0 <= x <= 0.3. For x = 0 the thermal-expansion coefficient
alpha(T) features a pronounced maximum around T = 50 K caused by a
temperature-dependent spin-state transition from a low-spin state (S=0) at low
temperatures towards a higher spin state of the Co^3+ ions. The partial
substitution of the La^3+ ions by divalent Ca^2+ ions causes drastic changes in
the macroscopic properties of LaCoO_3. Around x ~ 0.125 the large maximum in
alpha(T) has completely vanished. With further increasing x three different
anomalies develop
Oxygen, -element and iron abundance distributions in the inner part of the Galactic thin disc. II
We have derived the abundances of 36 chemical elements in one Cepheid star,
ASAS 181024--2049.6, located R kpc from the Galactic center.
This star falls within a region of the inner thin disc poorly sampled in
Cepheids. Our spectral analysis shows that iron, magnesium, silicon, calcium
and titanium LTE abundances in that star support the presence of a plateau-like
abundance distribution in the thin disc within 5 kpc of the Galactic center, as
previously suggested by \cite{Maret15}. If confirmed, the flattening of the
abundance gradient within that region could be the result of a decrease in the
star formation rate due to dynamic effects, possibly from the central Galactic
bar.Comment: 5 pages, 3 figure
First-principles Calculations of the Electronic Structure and Spectra of Strongly Correlated Systems: Dynamical Mean-field Theory
A recently developed dynamical mean-field theory in the iterated perturbation
theory approximation was used as a basis for construction of the "first
principles" calculation scheme for investigating electronic structure of
strongly correlated electron systems. This scheme is based on Local Density
Approximation (LDA) in the framework of the Linearized Muffin-Tin-Orbitals
(LMTO) method. The classical example of the doped Mott-insulator
La_{1-x}Sr_xTiO_3 was studied by the new method and the results showed
qualitative improvement in agreement with experimental photoemission spectra.Comment: 11 pages, 3 Postscript figures, LaTeX, submit in Journal of Physics:
Condensed Matte
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