4,236 research outputs found
Magnetic multipole analysis of kagome and artificial ice dipolar arrays
We analyse an array of linearly extended monodomain dipoles forming square
and kagome lattices. We find that its phase diagram contains two (distinct)
finite-entropy kagome ice regimes - one disordered, one algebraic - as well as
a low-temperature ordered phase. In the limit of the islands almost touching,
we find a staircase of corresponding entropy plateaux, which is analytically
captured by a theory based on magnetic charges. For the case of a modified
square ice array, we show that the charges ('monopoles') are excitations
experiencing two distinct Coulomb interactions: a magnetic 'three-dimensional'
one as well as a logarithmic `two dimensional' one of entropic origin.Comment: 4 pages, 2 figures; v2: minor changes as in final published versio
Paired composite fermion wavefunctions
We construct a family of BCS paired composite fermion wavefunctions that
generalize, but remain in the same topological phase as, the Moore-Read
Pfaffian state for the half-filled Landau level. It is shown that for a wide
range of experimentally relevant inter-electron interactions the groundstate
can be very accurately represented in this form.Comment: 4 pages, 2 figure
Paired composite fermion phase of quantum Hall bilayers at \nu = 1/2 + 1/2
We provide numerical evidence for composite fermion pairing in quantum Hall
bilayer systems at filling for intermediate spacing between the
layers. We identify the phase as pairing, and construct high
accuracy trial wavefunctions to describe the groundstate on the sphere. For
large distances between the layers, and for finite systems, a competing "Hund's
rule" state, or composite fermion liquid, prevails for certain system sizes. We
argue that for larger systems, the pairing phase will persist to larger layer
spacing.Comment: 4 pages, 2 figures; v2: final version, as published in journa
Dependence of direct neutron capture on nuclear-structure models
The prediction of cross sections for nuclei far off stability is crucial in
the field of nuclear astrophysics. We calculate direct neutron capture on the
even-even isotopes Sn and Pb with energy levels,
masses, and nuclear density distributions taken from different
nuclear-structure models. The utilized structure models are a
Hartree-Fock-Bogoliubov model, a relativistic mean field theory, and a
macroscopic-microscopic model based on the finite-range droplet model and a
folded-Yukawa single-particle potential. Due to the differences in the
resulting neutron separation and level energies, the investigated models yield
capture cross sections sometimes differing by orders of magnitude. This may
also lead to differences in the predicted astrophysical r-process paths.
Astrophysical implications are discussed.Comment: 25 pages including 12 figures, RevTeX, to appear in Phys. Rev.
Fractional Quantum Hall Effect of Lattice Bosons Near Commensurate Flux
We study interacting bosons on a lattice in a magnetic field. When the number of flux quanta per plaquette is close to a rational fraction, the low energy physics is mapped to a multi-species continuum model: bosons in the lowest Landau level where each boson is given an internal degree of freedom, or \emph{pseudospin}.
We find that the interaction potential between the bosons involves terms that do not conserve pseudospin, corresponding to umklapp processes, which in some cases
can also be seen as BCS-type pairing terms. We argue that in experimentally realistic regimes for bosonic atoms in optical lattices with synthetic magnetic fields, these terms are crucial for determining the nature of allowed ground states. In particular, we show numerically that certain paired wave functions related to the Moore-Read Pfaffian state are stabilized by these terms, whereas certain other wave functions can be destabilized when umklapp processes become strong
First decay study of the very neutron-rich isotope Br-93
The decay of the mass-separated, very neutron-rich isotope Br-93 has been
studied by gamma-spectroscopy. A level scheme of its daughter Kr-93 has been
constructed. Level energies, gamma-ray branching ratios and multipolarities
suggest spins and parities which are in accord with a smooth systematics of the
N=57 isotones for Z less-equal 40, suggesting the N=56 shell closure still to
be effective in Kr isotopes. So far, there is no indication of a progressive
onset of deformation in neutron-rich Kr isotopes.Comment: 17 pages, 3 figures, Phys. Rev. C, in prin
RPA approach to rotational symmetry restoration in a three-level Lipkin model
We study an extended Lipkin-Meshkov-Glick model that permits a transition to
a deformed phase with a broken continuous symmetry. Unlike simpler models, one
sees a persistent zero-frequency Goldstone mode past the transition point into
the deformed phase. We found that the RPA formula for the correlation energy
provides a useful correction to the Hartree-Fock energy when the number of
particle N satisfies N > 3, and becomes accurate for large N. We conclude that
the RPA correlation energy formula offers a promising way to improve the
Hartree-Fock energy in a systematic theory of nuclear binding energies.Comment: RevTex, 11 pages, 3 postscript figure
A Factorization Algorithm for G-Algebras and Applications
It has been recently discovered by Bell, Heinle and Levandovskyy that a large
class of algebras, including the ubiquitous -algebras, are finite
factorization domains (FFD for short).
Utilizing this result, we contribute an algorithm to find all distinct
factorizations of a given element , where is
any -algebra, with minor assumptions on the underlying field.
Moreover, the property of being an FFD, in combination with the factorization
algorithm, enables us to propose an analogous description of the factorized
Gr\"obner basis algorithm for -algebras. This algorithm is useful for
various applications, e.g. in analysis of solution spaces of systems of linear
partial functional equations with polynomial coefficients, coming from
. Additionally, it is possible to include inequality constraints
for ideals in the input
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