8,876 research outputs found
Observation of the dielectric-waveguide mode of light propagation in p-n junctions
Theoretical considerations of the propagation of electromagnetic energy near a p-n junction (1) show that the “sandwich” formed by having a depletion layer bounded by the p and n regions can act as a dielectric waveguide. (1,2
AIOCJ: A Choreographic Framework for Safe Adaptive Distributed Applications
We present AIOCJ, a framework for programming distributed adaptive
applications. Applications are programmed using AIOC, a choreographic language
suited for expressing patterns of interaction from a global point of view. AIOC
allows the programmer to specify which parts of the application can be adapted.
Adaptation takes place at runtime by means of rules, which can change during
the execution to tackle possibly unforeseen adaptation needs. AIOCJ relies on a
solid theory that ensures applications to be deadlock-free by construction also
after adaptation. We describe the architecture of AIOCJ, the design of the AIOC
language, and an empirical validation of the framework.Comment: Technical Repor
Flat-band ferromagnetism in a correlated topological insulator on a honeycomb lattice
We study the flat-band ferromagnetic phase of a spinfull and time-reversal
symmetric Haldane-Hubbard model on a honeycomb lattice within a bosonization
formalism for flat-band Z topological insulators. Such a study extend our
previous one [L. S. G. Leite and R. L. Doretto, Phys. Rev. B {\bf 104}, 155129
(2021)] concerning the flat-band ferromagnetic phase of a correlated Chern
insulator described by a Haldane-Hubbard model. We consider the topological
Hubbard model at filling of its corresponding noninteracting limit and in
the nearly flat band limit of its lower free-electronic bands. We show that it
is possible to define boson operators associated with two distinct spin-flip
excitations, one that changes (mixed-lattice excitations) and a second one that
preserves (same-lattice excitations) the index related with the two triangular
sublattices. Within the bosonization scheme, the fermionic model is mapped into
an effective interacting boson model, whose quadratic term is considered at the
harmonic approximation in order to determine the spin-wave excitation spectrum.
For both mixed and same-lattice excitations, we find that the spin-wave
spectrum is gapped and has two branches, with an energy gap between the lower
and the upper bands at the and points of the first Brillouin zone.
Such a behavior is distinct from the one of the corresponding correlated Chern
insulator, whose spin-wave spectrum has a Goldstone mode at the center of the
first Brillouin zone and Dirac points at and points. We also find some
evidences that the spin-wave bands for the same-lattice excitations might be
topologically nontrivial even in the completely flat band limit.Comment: 16 pages, 8 figures, companion paper to our previous
arXiv:2106.00468, final versio
Flat-band ferromagnetism and spin waves in the Haldane-Hubbard model
We study the flat-band ferromagnetic phase of the Haldane-Hubbard model on a
honeycomb lattice within a bosonization scheme for flat-band Chern insulators,
focusing on the calculation of the spin-wave excitation spectrum. We consider
the Haldane-Hubbard model with the noninteracting lower bands in a nearly-flat
band limit, previously determined for the spinless model, and at 1/4-filling of
its corresponding noninteracting limit. Within the bosonization scheme, the
Haldane-Hubbard model is mapped into an effective interacting boson model,
whose quadratic term allows us to determine the spin-wave spectrum at the
harmonic approximation. We show that the excitation spectrum has two branches
with a Goldstone mode and Dirac points at center and at the K and K' points of
the first Brillouin zone, respectively. We also consider the effects on the
spin-wave spectrum due to an energy offset in the on-site Hubbard repulsion
energies and due to the presence of an staggered on-site energy term, both
quantities associated with the two triangular sublattices. In both cases, we
find that an energy gap opens at the K and K' points. Moreover, we also find
some evidences for an instability of the flat-band ferromagnetic phase in the
presence of the staggered on-site energy term. We provide some additional
results for the square lattice topological Hubbard model previous studied
within the bosonization formalism and comment on the differences between the
bosonization scheme implementation for the correlated Chern insulators on both
square and honeycomb lattices.Comment: 17 pages, 11 figure
Entanglement entropy for the valence bond solid phases of two-dimensional dimerized Heisenberg antiferromagnets
We calculate the bipartite von Neumann and second R\'enyi entanglement
entropies of the ground states of spin-1/2 dimerized Heisenberg
antiferromagnets on a square lattice. Two distinct dimerization patterns are
considered: columnar and staggered. In both cases, we concentrate on the
valence bond solid (VBS) phase and describe such a phase with the bond-operator
representation. Within this formalism, the original spin Hamiltonian is mapped
into an effective interacting boson model for the triplet excitations. We study
the effective Hamiltonian at the harmonic approximation and determine the
spectrum of the elementary triplet excitations. We then follow an analytical
procedure, which is based on a modified spin-wave theory for finite systems and
was originally employed to calculate the entanglement entropies of magnetic
ordered phases, and calculate the entanglement entropies of the VBS ground
states. In particular, we consider one-dimensional (line) subsystems within the
square lattice, a choice that allows us to consider line subsystems with sizes
up to . We combine such a procedure with the results of the
bond-operator formalism at the harmonic level and show that, for both dimerized
Heisenberg models, the entanglement entropies of the corresponding VBS ground
states obey an area law as expected for gapped phases. For both columnar-dimer
and staggered-dimer models, we also show that the entanglement entropies
increase but do not diverge as the dimerization decreases and the system
approaches the N\'eel--VBS quantum phase transition. Finally, the entanglement
spectra associated with the VBS ground states are presented.Comment: 14 pages, 9 figure
Divergência genética entre acessos do banco ativo de germoplasma de cebola da Embrapa Clima Temperado revelada por marcadores RAPD.
bitstream/item/30465/1/boletim-81.pd
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