18,872 research outputs found
Anisotropy and percolation threshold in a multifractal support
Recently a multifractal object, , was proposed to study percolation
properties in a multifractal support. The area and the number of neighbors of
the blocks of show a non-trivial behavior. The value of the
probability of occupation at the percolation threshold, , is a function
of , a parameter of which is related to its anisotropy. We
investigate the relation between and the average number of neighbors of
the blocks as well as the anisotropy of
Group theory for structural analysis and lattice vibrations in phosphorene systems
Group theory analysis for two-dimensional elemental systems related to
phosphorene is presented, including (i) graphene, silicene, germanene and
stanene, (ii) dependence on the number of layers and (iii) two stacking
arrangements. Departing from the most symmetric graphene space
group, the structures are found to have a group-subgroup relation, and analysis
of the irreducible representations of their lattice vibrations makes it
possible to distinguish between the different allotropes. The analysis can be
used to study the effect of strain, to understand structural phase transitions,
to characterize the number of layers, crystallographic orientation and
nonlinear phenomena.Comment: 24 pages, 3 figure
Origin and spectroscopic determination of trigonal anisotropy in a heteronuclear single-molecule magnet
W-band ({\nu} ca. 94 GHz) electron paramagnetic resonance (EPR) spectroscopy
was used for a single-crystal study of a star-shaped Fe3Cr single-molecule
magnet (SMM) with crystallographically imposed trigonal symmetry. The high
resolution and sensitivity accessible with W-band EPR allowed us to determine
accurately the axial zero-field splitting terms for the ground (S =6) and first
two excited states (S =5 and S =4). Furthermore, spectra recorded by applying
the magnetic field perpendicular to the trigonal axis showed a pi/6 angular
modulation. This behavior is a signature of the presence of trigonal transverse
magnetic anisotropy terms whose values had not been spectroscopically
determined in any SMM prior to this work. Such in-plane anisotropy could only
be justified by dropping the so-called 'giant spin approach' and by considering
a complete multispin approach. From a detailed analysis of experimental data
with the two models, it emerged that the observed trigonal anisotropy directly
reflects the structural features of the cluster, i.e., the relative orientation
of single-ion anisotropy tensors and the angular modulation of single-ion
anisotropy components in the hard plane of the cluster. Finally, since
high-order transverse anisotropy is pivotal in determining the spin dynamics in
the quantum tunneling regime, we have compared the angular dependence of the
tunnel splitting predicted by the two models upon application of a transverse
field (Berry-phase interference).Comment: 13 pages, 9 figure
Criação de Chrysoperla externa para o controle biológico de pragas do algodoeiro.
bitstream/CNPA-2009-09/14457/1/CIRTEC36.pd
On the quantumness of correlations in nuclear magnetic resonance
Nuclear Magnetic Resonance (NMR) was successfully employed to test several
protocols and ideas in Quantum Information Science. In most of these
implementations the existence of entanglement was ruled out. This fact
introduced concerns and questions about the quantum nature of such bench tests.
In this article we address some issues related to the non-classical aspects of
NMR systems. We discuss some experiments where the quantum aspects of this
system are supported by quantum correlations of separable states. Such
quantumness, beyond the entanglement-separability paradigm, is revealed via a
departure between the quantum and the classical versions of information theory.
In this scenario, the concept of quantum discord seems to play an important
role. We also present an experimental implementation of an analogous of the
single-photon Mach-Zehnder interferometer employing two nuclear spins to encode
the interferometric paths. This experiment illustrate how non-classical
correlations of separable states may be used to simulate quantum dynamics. The
results obtained are completely equivalent to the optical scenario, where
entanglement (between two field modes) may be present
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