78,609 research outputs found
Scattering invisibility with free-space field enhancement of all-dielectric nanoparticles
Simultaneous scattering invisibility and free-space field enhancement have
been achieved based on multipolar interferences among all-dielectric
nanoparticles. The scattering properties of all-dielectric nanowire quadrumers
are investigated and two sorts of scattering invisibilities have been
identified: the trivial invisibility where the individual nanowires are not
effectively excited; and the nontrivial invisibility with strong multipolar
excitations within each nanowire, which results in free-space field enhancement
outside the particles. It is revealed that such nontrivial invisibility
originates from not only the simultaneous excitations of both electric and
magnetic resonances, but also their significant magnetoelectric
cross-interactions. We further show that the invisibility obtained is both
polarization and direction selective, which can probably play a significant
role in various applications including non-invasive detection, sensing, and
non-disturbing medical diagnosis with high sensitivity and precision.Comment: 7 pages, 4 figures and comments are welcom
Pseudoscalar or vector meson production in non-leptonic decays of heavy hadrons
We have addressed the study of non-leptonic weak decays of heavy hadrons
( and ), with external and internal emission to
give two final hadrons, taking into account the spin-angular momentum structure
of the mesons and baryons produced.
A detailed angular momentum formulation is developed which leads to easy
final formulas. By means of them we have made predictions for a large amount of
reactions, up to a global factor, common to many of them, that we take from
some particular data. Comparing the theoretical predictions with the
experimental data, the agreement found is quite good in general and the
discrepancies should give valuable information on intrinsic form factors,
independent of the spin structure studied here. The formulas obtained are also
useful in order to evaluate meson-meson or meson-baryon loops, for instance of
decays, in which one has PP, PV, VP or VV intermediate states, with P for
pseudoscalar mesons and V for vector meson and lay the grounds for studies of
decays into three final particles.Comment: 54 pages, 7 figures, 13 tables; v2: 60 pages, 9 figures, 14 tables,
discussion added, references added, version to appear in Eur.Phys.J.
Unified Picture for Magnetic Correlations in Iron-Based Superconductors
The varying metallic antiferromagnetic correlations observed in iron-based
superconductors are unified in a model consisting of both itinerant electrons
and localized spins. The decisive factor is found to be the sensitive
competition between the superexchange antiferromagnetism and the
orbital-degenerate double-exchange ferromagnetism. Our results reveal the
crucial role of Hund's rule coupling for the strongly correlated nature of the
system and suggest that the iron-based superconductors are closer kin to
manganites than cuprates in terms of their diverse magnetism and incoherent
normal-state electron transport. This unified picture would be instrumental for
exploring other exotic properties and the mechanism of superconductivity in
this new class of superconductors.Comment: Revised for publication. 3 figure
Charge Ordering in Half-Doped Manganites: Weak Charge Disproportion and Leading Mechanisms
The apparent contradiction between the recently observed weak charge
disproportion and the traditional Mn/Mn picture of the
charge-orbital orders in half-doped manganites is resolved by a novel Wannier
states analysis of the LDA electronic structure. Strong electron itinerancy
in this charge-transfer system significantly delocalizes the occupied
low-energy "Mn" Wannier states such that charge leaks into the
"Mn"-sites. Furthermore, the leading mechanisms of the charge order are
quantified via our first-principles derivation of the low-energy effective
Hamiltonian. The electron-electron interaction is found to play a role as
important as the electron-lattice interaction. \ignore{A general picture of
doped holes in strongly correlated charge-transfer systems is presented and
applied to the study of charge order in half-doped manganites, using a novel
Wannier states analysis of the LDA electronic structure. While residing
primarily in the oxygen atoms, the doped holes form additional effective
orbitals at the low-energy scale, leading to an effective Mn/Mn
valence picture that enables weak charge disproportion, resolving the current
serious contradictions between the recent experimental observations of charge
distribution and traditional models. Furthermore, the leading mechanisms of the
observed charge order are quantified via our first-principles derivation of the
low-energy effective HamiltonianComment: accepted by Europhysics Letter
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