An adaptive algorithm for n-body field expansions
Weinberg, Martin D.
1998-05-28
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18 records were found.
The zero temperature Mott transition region in antiferromagnetic, spin S=5/2
MnO is probed using the correlated band theory LSDA+U method. The first
transition encountered is an insulator-insulator volume collapse within the
rocksalt structure that is characterized by an unexpected Hund's rule violating
`spin-flip' moment collapse. This spin-flip to S=1/2 takes fullest advantage of
the anisotropy of the Coulomb repulsion, allowing gain in the kinetic energy
(which increases with decreasing volume) while retaining a sizable amount of
the magnetic exchange energy. While transition pressures vary with the
interaction strength, the spin-flip state is robust over a range of interaction
strengths and for both B1 and B8 structures.
Thermoelectric effects enable the direct conversion between thermal and
electrical energy and provide an alternative route for power generation and
refrigeration. The clathrate Ba8Ga16Ge30 has the highest figure of merit (ZT ~
1) among other members in the family of type-I inorganic clathrates.
Enhancement of the thermoelectric properties have been observed in multilayered
superlattices, quantum wires and in nanostructured materials, either due to the
increase in power-factor (S^{2}\sigma) or due to the reduction of lattice
thermal conductivity (\kappa). Here, we investigate the thermoelectric
properties of two-dimensional slabs with varying thickness of Ba8Ga16Ge30 using
semi-classical Boltzmann transport theory with constant scattering
approximation. We observe that, there exists a delicate balance between the
electrical conductivi...
Comment: 9 pages, 8 figures. Accepted in PRB 2008
Comment: 6 pages, 5 figures, 1 table
Comment: 8 pages, 8 figures
The magnetic nature of Cs$_{2}$AgF$_{4}$, an isoelectronic and isostructural
analogue of La$_2$CuO$_4$, is analyzed using density functional calculations.
The ground state is found to be ferromagnetic and nearly half metallic. We find
strong hybridization of Ag-$d$ and F-$p$ states. Substantial moments reside on
the F atoms, which is unusual for the halides and reflects the chemistry of the
Ag(II) ions in this compound. This provides the mechanism for ferromagnetism,
which we find to be itinerant in character, a result of a Stoner instability
enhanced by Hund's coupling on the F.
Comment: PRB Accepted, 11 pages, 10 figures
We have grown single crystals of EuFe2As2 and investigated its electrical
transport and thermodynamic properties. Electrical resistivity and specific
heat measurements clearly establish the intrinsic nature of magnetic phase
transitions at 20 K and 195 K. While the high temperature phase transition is
associated with the itinerant moment of Fe, the low temperature phase
transition is due to magnetic order of localized Eu-moments. Band structure
calculations point out a very close similarity of the electronic structure with
SrFe2As2. Magnetically, the Eu and Fe2As2 sublattice are nearly de-coupled.
