157 research outputs found
Electronic theory for superconductivity in SrRuO: triplet pairing due to spin-fluctuation exchange
Using a two-dimensional Hubbard Hamiltonian for the three electronic bands
crossing the Fermi level in SrRuO we calculate the band structure and
spin susceptibility in quantitative agreement with
nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS)
experiments. The susceptibility has two peaks at {\bf Q}
due to the nesting Fermi surface properties and at {\bf q}
due to the tendency towards ferromagnetism. Applying spin-fluctuation exchange
theory as in layered cuprates we determine from ,
electronic dispersions, and Fermi surface topology that superconductivity in
SrRuO consists of triplet pairing. Combining the Fermi surface topology
and the results for we can exclude and wave
symmetry for the superconducting order parameter. Furthermore, within our
analysis and approximations we find that -wave symmetry is slightly favored
over p-wave symmetry due to the nesting properties of the Fermi surface.Comment: 5 pages, 5 figures, misprints correcte
Spin-triplet superconductivity due to antiferromagnetic spin-fluctuation in Sr_2RuO_4
A mechanism leading to the spin-triplet superconductivity is proposed based
on the antiferromagnetic spin fluctuation. The effects of anisotropy in spin
fluctuation on the Cooper pairing and on the direction of d vector are examined
in the one-band Hubbard model with RPA approximation. The gap equations for the
anisotropic case are derived and applied to Sr_2RuO_4. It is found that a
nesting property of the Fermi surface together with the anisotropy leads to the
triplet superconductivity with the d=z(sin{k_x}\pm isin{k_y}), which is
consistent with experiments.Comment: 4 pages, 3 eps figures, revte
Scale-dependent Galaxy Bias
We present a simple heuristic model to demonstrate how feedback related to
the galaxy formation process can result in a scale-dependent bias of mass
versus light, even on very large scales. The model invokes the idea that
galaxies form initially in locations determined by the local density field, but
the subsequent formation of galaxies is also influenced by the presence of
nearby galaxies that have already formed. The form of bias that results
possesses some features that are usually described in terms of stochastic
effects, but our model is entirely deterministic once the density field is
specified. Features in the large-scale galaxy power spectrum (such as wiggles
that might in an extreme case mimic the effect of baryons on the primordial
transfer function) could, at least in principle, arise from spatial modulations
of the galaxy formation process that arise naturally in our model. We also show
how this fully deterministic model gives rise to apparently stochasticity in
the galaxy distribution.Comment: 14 pages, 2 figures, typos corrected, discussion added and references
corrected; matches version accepted by JCA
Arbitrary Choice of Basic Variables in Density Functional Theory. II. Illustrative Applications
Our recent theory (Ref. 1) enables us to choose arbitrary quantities as the
basic variables of the density functional theory. In this paper we apply it to
several cases. In the case where the occupation matrix of localized orbitals is
chosen as a basic variable, we can obtain the single-particle equation which is
equivalent to that of the LDA+U method. The theory also leads to the
Hartree-Fock-Kohn-Sham equation by letting the exchange energy be a basic
variable. Furthermore, if the quantity associated with the density of states
near the Fermi level is chosen as a basic variable, the resulting
single-particle equation includes the additional potential which could mainly
modify the energy-band structures near the Fermi level.Comment: 27 page
Neo-Newtonian cosmology: An intermediate step towards General Relativity
Cosmology is a field of physics in which the use of General Relativity theory
is indispensable. However, a cosmology based on Newtonian gravity theory for
gravity is possible in certain circumstances. The applicability of Newtonian
theory can be substantially extended if it is modified in such way that
pressure has a more active role as source of the gravitational field. This was
done in the neo-Newtonian cosmology. The limitation on the construction of a
Newtonian cosmology, and the need for a relativistic theory in cosmology are
reviewed. The neo-Newtonian proposal is presented, and its consequences for
cosmology are discussed.Comment: 10 pages. Portuguese version submitted to RBE
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