130 research outputs found
Role of Coulomb correlation on magnetic and transport properties of doped manganites: La0.5Sr0.5MnO3 and LaSr2Mn2O7
Results of LSDA and LSDA+U calculations of the electronic structure and
magnetic configurations of the 50% hole-doped pseudocubic perovskite
La0.5Sr0.5MnO3 and double layered LaSr2Mn2O7 are presented. We demonstrate that
the on-site Coulomb correlation (U) of Mn d electrons has a very different
influence on the (i) band formations, (ii) magnetic ground states, (iii)
interlayer exchange interactions, and (iv) anisotropy of the electrical
transport in these two manganites. A possible reason why the LSDA failures in
predicting observed magnetic and transport properties of the double layered
compound - in contrast to the doped perovskite manganite - is considered on the
basis of a p-d hybridization analysis.Comment: 11 pages, 3 figure
Coulomb correlation and magnetic ordering in double-layered manganites: LaSrMnO
A detailed study of the electronic structure and magnetic configurations of
the 50 % hole-doped double layered manganite LaSrMnO is presented.
We demonstrate that the on-site Coulomb correlation (U) of Mn d electrons {\it
(i)} significantly modifies the electronic structure, magnetic ordering (from
FM to AFM), and interlayer exchange interactions, and {\it (ii)} promotes
strong anisotropy in electrical transport, reducing the effective hopping
parameter along the {\it c} axis for electrically active electrons. This
findng is consistent with observations of anisotropic transport -- a property
which sets this manganite apart from conventional 3D systems. A half-metallic
band structure is predicted with both the LSDA and LSDA+U methods. The
experimentally observed A-type AFM ordering in LaSrMnO is found to
be energetically more favorable with U 7 eV. A simple interpretation of
interlayer exchange coupling is given within double and super-exchange
mechanisms based on the dependencies on U of the effective exchange parameters
and state sub-band widths.Comment: 10 pages, 5 figure
Long-term trends in the longevity of scientific elites: evidence from the British and the Russian academies of science.
National science academies represent intellectual elites and vanguard groups in the achievement of longevity. We estimated life expectancy (LE) at age 50 of members of the British Royal Society (RS) for the years 1670-2007 and of members of the Russian Academy of Sciences (RAS) for the years 1750-2006. The longevity of academicians was higher than that of their corresponding national populations, with the gap widening from the 1950s. Since the 1980s, LE in the RS has been higher than the maximum LE among all high-income countries. In each period, LE in the RS was greater than in the RAS, although since the 1950s it has risen in parallel in the two academies. This steep increase shared by academicians in Britain and Russia suggests that general populations have the potential for a substantial increase in survival to high ages
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