8,379 research outputs found
Microscopic Model of Cuprate Superconductivity
We present a model for cuprate superconductivity based on the identification
of an experimentally detected "local superconductor" as a charge 2 fermion
pairing in a circular, stationary density wave. This wave acts like a highly
correlated local "boson" satisfying a modified Cooper problem with additional
correlation stabilization relative to the separate right- and left-handed
density waves composing it. This local "boson" could be formed in a two-bound
roton-like manner; it has Fermion statistics. Delocalized superconductive
pairing (superconductivity) is achieved by a Feshbach resonance of two unpaired
holes (electrons) resonating with a virtual energy level of the bound pair
state of the local "boson" as described by the Boson-Fermion-Gossamer (BFG)
model. The spin-charge order interaction offers an explanation for the overall
shape of the superconducting dome as well a microscopic basis for the cuprate
superconducting transition temperatures. An explanation of the correlation of
superconducting transition temperature with experimental inelastic neutron and
electron Raman scattering is proposed, based on the energy of the virtual bound
pair. These and other modifications discussed suggest a microscopic explanation
for the entire cuprate superconductivity dome shape.Comment: 27 pages, 7 figures, presented at the 50th Sanibel Symposiu
A proposed generalization of Emden's differential equation to embrace the ground-state electronic structure of extremely heavy positive atomic ions with and without applied magnetic fields
Integral equation for inhomogeneous condensed bosons generalizing the Gross-Pitaevskii differential equation
We give here the derivation of a Gross-Pitaevskii--type equation for
inhomogeneous condensed bosons. Instead of the original Gross-Pitaevskii
differential equation, we obtain an integral equation that implies less
restrictive assumptions than are made in the very recent study of Pieri and
Strinati [Phys. Rev. Lett. 91 (2003) 030401]. In particular, the Thomas-Fermi
approximation and the restriction to small spatial variations of the order
parameter invoked in their study are avoided.Comment: Phys. Rev. A (accepted
Superconducting transition temperatures of the elements related to elastic constants
For a given crystal structure, say body-centred-cubic, the many-body
Hamiltonian in which nuclear and electron motions are to be treated from the
outset on the same footing, has parameters, for the elements, which can be
classified as (i) atomic mass M, (ii) atomic number Z, characterizing the
external potential in which electrons move, and (iii) bcc lattice spacing, or
equivalently one can utilize atomic volume, Omega. Since the thermodynamic
quantities can be determined from H, we conclude that Tc, the superconducting
transition temperature, when it is non-zero, may be formally expressed as Tc =
Tc^(M) (Z, Omega). One piece of evidence in support is that, in an atomic
number vs atomic volume graph, the superconducting elements lie in a well
defined region. Two other relevant points are that (a) Tc is related by BCS
theory, though not simply, to the Debye temperature, which in turn is
calculable from the elastic constants C_{11}, C_{12}, and C_{44}, the atomic
weight and the atomic volume, and (b) Tc for five bcc transition metals is
linear in the Cauchy deviation C* = (C_{12} - C_{44})/(C_{12} + C_{44}).
Finally, via elastic constants, mass density and atomic volume, a correlation
between C* and the Debye temperature is established for the five bcc transition
elements.Comment: EPJB, accepte
Particle density and non-local kinetic energy density functional for two-dimensional harmonically confined Fermi vapors
We evaluate analytically some ground state properties of two-dimensional
harmonically confined Fermi vapors with isotropy and for an arbitrary number of
closed shells. We first derive a differential form of the virial theorem and an
expression for the kinetic energy density in terms of the fermion particle
density and its low-order derivatives. These results allow an explicit
differential equation to be obtained for the particle density. The equation is
third-order, linear and homogeneous. We also obtain a relation between the
turning points of kinetic energy and particle densities, and an expression of
the non-local kinetic energy density functional.Comment: 7 pages, 2 figure
Topology, connectivity and electronic structure of C and B cages and the corresponding nanotubes
After a brief discussion of the structural trends which appear with
increasing number of atoms in B cages, a one-to one correspondence between the
connectivity of B cages and C cage structures will be proposed. The electronic
level spectra of both systems from Hartree-Fock calculations is given and
discussed. The relation of curvature introduced into an originally planar
graphitic fragment to pentagonal 'defects' such as are present in
buckminsterfullerene is also briefly treated.
A study of the structure and electronic properties of B nanotubes will then
be introduced. We start by presenting a solution of the free-electron network
approach for a 'model boron' planar lattice with local coordination number 6.
In particular the dispersion relation E(k) for the pi-electron bands, together
with the corresponding electronic Density Of States (DOS), will be exhibited.
This is then used within the zone folding scheme to obtain information about
the electronic DOS of different nanotubes obtained by folding this model boron
sheet.
To obtain the self-consistent potential in which the valence electrons move
in a nanotube, 'the March model' in its original form was invoked and results
are reported for a carbon nanotube.
Finally, heterostructures, such as BN cages and fluorinated
buckminsterfullerene, will be briefly treated, the new feature here being
electronegativity difference.Comment: 22 pages (revtex4) 12 figure
Exquisitively sensitive matter-wave interferometry used to measure the change in velocity of a moving magnet traversing an electric field
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