1,526 research outputs found
Transport properties and electronic states of the thermoelectric oxide NaCo_2O_4
Physical properties of the thermoelectric oxide NaCo_2O_4 are briefly
reviewed. The high thermoelectric properties of this material are attributed to
the substantially enhanced effective mass, which comes from the large entropy
of Co in the low spin state. The large entropy confined in the CoO_2
block causes a spin-density-wave transition at 22 K upon Cu substitution for
Co, which can be regarded as ``order from disorder''.Comment: 4 Pages, $ figures, Proceedings of The 2nd Hiroshima Workshop:
Transport and Thermal Properties of Advanced Material
Electronic band structure and Fermi surface of AgPbO
We present electronic band structure of AgPbO with layered
hexagonal structure containing one-dimensional chains and two-dimensional
Kagom\'{e} layers of silver. A half-filled conduction band shows extremely
simple, single nearly-free-electron-like Fermi surface. The conduction band is
composed of an antibonding state of Pb- and O- mixing with Ag-4d and
. Mass enhancement in the state density at the Fermi energy is expected to
be negligibly small by comparing with the specific-heat data. Calculated Fermi
velocity is consistent with small anisotropy observed in transport properties.
Doping effects on the electronic structure are also discussed.Comment: 6 pages, 9 figures; fig7 replaced, reference 6 adde
Study of the triangular lattice tV model near x=1/3
We study extended Hubbard model on a triangular lattice near doping ,
which may be relevant for the recently discovered superconductor NaCoOHO. By generalizing this model to fermionic species, we
formulate a meanfield description in the limit of large . In meanfield, we
find two possible phases: a renormalized Fermi liquid and a \rt3rt3 charge
density wave state. The transition between the two phases is driven by
increasing the nearest neighbor repulsion and is found to be first order for
doping , but occurs close to the point of the local instability of the
uniform liquid. We also study fluctuations about the uniform meanfield state in
a systematic 1/N expansion, focusing on the residual interaction of
quasiparticles and possible superconducting instabilities due to this
interaction. Upon moving towards the CDW instability, the increasing charge
fluctuations favor a particular -wave triplet state. (This state was
recently discussed by Tanakaet al, cond-mat/0311266). We also report a direct
Gutzwiller wavefunction study of the spin-1/2 model.Comment: 9 pages, 5 figure
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