5,281 research outputs found
Bosonic versus fermionic pairs of topological spin defects in monolayered high-T_c superconductors
The energy associated with bosonic and fermionic pairs of topological spin
defects in doped antiferromagnetic quantum spin-1/2 square lattice is estimated
within a resonating valence bond scenario, as described by a t-t'-J-like model
Hamiltonian, plus a t-perpendicular, responsible of a three-dimensional
screening of the electrostatic repulsion within the bosonic pairs. For
parameters appropriate for monolayered high-T_c superconductors, both fermionic
and bosonic pairs show x^2-y^2 symmetry. We find a critical value of doping
such that the energy of the bosonic pairs goes below twice the energy of two
fermionic pairs at their Fermi level. This finding could be related to the
onset of high-T_c superconductivity.Comment: 10 pages, 6 figures. To be published in Phys. Rev.
Exponential localization of hydrogen-like atoms in relativistic quantum electrodynamics
We consider two different models of a hydrogenic atom in a quantized
electromagnetic field that treat the electron relativistically. The first one
is a no-pair model in the free picture, the second one is given by the
semi-relativistic Pauli-Fierz Hamiltonian. We prove that the no-pair operator
is semi-bounded below and that its spectral subspaces corresponding to energies
below the ionization threshold are exponentially localized. Both results hold
true, for arbitrary values of the fine-structure constant, , and the
ultra-violet cut-off, , and for all nuclear charges less than the
critical charge without radiation field, . We obtain
similar results for the semi-relativistic Pauli-Fierz operator, again for all
values of and and for nuclear charges less than .Comment: 37 page
Correlations in atomic systems: Diagnosing coherent superpositions
While investigating quantum correlations in atomic systems, we note that
single measurements contain information about these correlations. Using a
simple model of measurement -- analogous to the one used in quantum optics --
we show how to extract higher order correlation functions from individual
"phtotographs" of the atomic sample. As a possible application we apply the
method to detect a subtle phase coherence in mesoscopic superpostitions.Comment: 4 pages, 2 figures, provisionally accepted to Physical Review Letter
There are No Unfilled Shells in Hartree-Fock Theory
Hartree-Fock theory is supposed to yield a picture of atomic shells which may
or may not be filled according to the atom's position in the periodic table. We
prove that shells are always completely filled in an exact Hartree-Fock
calculation. Our theorem generalizes to any system having a two-body
interaction that, like the Coulomb potential, is repulsive.Comment: 5 pages, VBEHLMLJPS--16/July/9
Characterization of Spatial Coherence of Synchrotron Radiation with Non-Redundant Arrays of Apertures
We present a method to characterize the spatial coherence of soft X-ray
radiation from a single diffraction pattern. The technique is based on
scattering from non-redundant arrays (NRA) of slits and records the degree of
spatial coherence at several relative separations from one to 15 microns,
simultaneously. Using NRAs we measured the transverse coherence of the X-ray
beam at the XUV X-ray beamline P04 of the PETRA III synchrotron storage ring as
a function of different beam parameters. To verify the results obtained with
the NRAs additional Young's double pinhole experiments were conducted and show
good agreement.Comment: 15 pages, 6 figures, 2 tables, 42 reference
Estimating the Electricity Prices, Generation Costs and CO2 Emissions of Large Scale Wind Energy Exports from Ireland to Great Britain
The share of wind generation in the Irish and British electricity markets is set to increase by 2020 due to renewable energy (RE) targets. The United Kingdom (UK) and Ireland have set ambitious targets which require 30% and 40% of electricity demand to come from RE, mainly wind, by 2020, respectively. Ireland has sufficient indigenous onshore wind energy resources to exceed the RE target, while the UK faces uncertainty in achieving its target. A possible solution for the UK is to import RE directly from large scale onshore and offshore wind energy projects in Ireland; this possibility has recently been explored by both governments but is currently on hold. Thus, the aim of this paper is to estimate the effects of large scale wind energy in the Irish and British electricity markets in terms of wholesale system marginal prices, total generation costs and CO2 emissions. The results indicate when the large scale Irish-based wind energy projects are connected directly to the UK there is a decrease of 0.6% and 2% in the Irish and British wholesale system marginal prices under the UK National Grid slow progression scenario, respectively
The mass shell in the semi-relativistic Pauli-Fierz model
We consider the semi-relativistic Pauli-Fierz model for a single free
electron interacting with the quantized radiation field. Employing a variant of
Pizzo's iterative analytic perturbation theory we construct a sequence of
ground state eigenprojections of infra-red cutoff, dressing transformed fiber
Hamiltonians and prove its convergence, as the cutoff goes to zero. Its limit
is the ground state eigenprojection of a certain Hamiltonian unitarily
equivalent to a renormalized fiber Hamiltonian acting in a coherent state
representation space. The ground state energy is an exactly two-fold degenerate
eigenvalue of the renormalized Hamiltonian, while it is not an eigenvalue of
the original fiber Hamiltonian unless the total momentum is zero. These results
hold true, for total momenta inside a ball about zero of arbitrary radius p>0,
provided that the coupling constant is sufficiently small depending on p and
the ultra-violet cutoff. Along the way we prove twice continuous
differentiability and strict convexity of the ground state energy as a function
of the total momentum inside that ball.Comment: 44 page
Gapless Excitation above a Domain Wall Ground State in a Flat Band Hubbard Model
We construct a set of exact ground states with a localized ferromagnetic
domain wall and with an extended spiral structure in a deformed flat-band
Hubbard model in arbitrary dimensions. We show the uniqueness of the ground
state for the half-filled lowest band in a fixed magnetization subspace. The
ground states with these structures are degenerate with all-spin-up or
all-spin-down states under the open boundary condition. We represent a spin
one-point function in terms of local electron number density, and find the
domain wall structure in our model. We show the existence of gapless
excitations above a domain wall ground state in dimensions higher than one. On
the other hand, under the periodic boundary condition, the ground state is the
all-spin-up or all-spin-down state. We show that the spin-wave excitation above
the all-spin-up or -down state has an energy gap because of the anisotropy.Comment: 26 pages, 1 figure. Typos are fixe
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