27,715 research outputs found
Dimensionality effects in the LDOS of ferromagnetic hosts probed via STM: spin-polarized quantum beats and spin filtering
We theoretically investigate the local density of states (LDOS) probed by a
STM tip of ferromagnetic metals hosting a single adatom and a subsurface
impurity. We model the system via the two-impurity Anderson Hamiltonian. By
using the equation of motion with the relevant Green functions, we derive
analytical expressions for the LDOS of two host types: a surface and a quantum
wire. The LDOS reveals Friedel-like oscillations and Fano interference as a
function of the STM tip position. These oscillations strongly depend on the
host dimension. Interestingly, we find that the spin-dependent Fermi wave
numbers of the hosts give rise to spin-polarized quantum beats in the LDOS.
While the LDOS for the metallic surface shows a damped beating pattern, it
exhibits an opposite behavior in the quantum wire. Due to this absence of
damping, the wire operates as a spatially resolved spin filter with a high
efficiency.Comment: revised tex
Localization properties of a tight-binding electronic model on the Apollonian network
An investigation on the properties of electronic states of a tight-binding
Hamiltonian on the Apollonian network is presented. This structure, which is
defined based on the Apollonian packing problem, has been explored both as a
complex network, and as a substrate, on the top of which physical models can
defined. The Schrodinger equation of the model, which includes only nearest
neighbor interactions, is written in a matrix formulation. In the uniform case,
the resulting Hamiltonian is proportional to the adjacency matrix of the
Apollonian network. The characterization of the electronic eigenstates is based
on the properties of the spectrum, which is characterized by a very large
degeneracy. The rotation symmetry of the network and large number of
equivalent sites are reflected in all eigenstates, which are classified
according to their parity. Extended and localized states are identified by
evaluating the participation rate. Results for other two non-uniform models on
the Apollonian network are also presented. In one case, interaction is
considered to be dependent of the node degree, while in the other one, random
on-site energies are considered.Comment: 7pages, 7 figure
Generalized entropy arising from a distribution of q-indices
It is by now well known that the Boltzmann-Gibbs (BG) entropy
can be usefully generalized into the
entropy (). Microscopic dynamics determines, given classes of initial
conditions, the occupation of the accessible phase space (or of a
symmetry-determined nonzero-measure part of it), which in turn appears to
determine the entropic form to be used. This occupation might be a uniform one
(the usual {\it equal probability hypothesis} of BG statistical mechanics),
which corresponds to ; it might be a free-scale occupancy, which appears
to correspond to . Since occupancies of phase space more complex than
these are surely possible in both natural and artificial systems, the task of
further generalizing the entropy appears as a desirable one, and has in fact
been already undertaken in the literature. To illustrate the approach, we
introduce here a quite general entropy based on a distribution of -indices
thus generalizing . We establish some general mathematical properties for
the new entropic functional and explore some examples. We also exhibit a
procedure for finding, given any entropic functional, the -indices
distribution that produces it. Finally, on the road to establishing a quite
general statistical mechanics, we briefly address possible generalized
constraints under which the present entropy could be extremized, in order to
produce canonical-ensemble-like stationary-state distributions for Hamiltonian
systems.Comment: 14 pages including 3 figure
Caracterização anatômica de frutos de genótipos de bananeira quanto ao despencamento.
As bananas são comercializadas em pencas ou buquês, geralmente com 4 a 9 frutos, sendo o despencamento dos frutos um dos principais problemas na comercialização, fazendo com que ocorra diminuição da aceitação dos consumidores e, consequentemente, diminuição do valor de mercado da fruta. Este despencamento dos frutos é uma desordem fisiológica pós-colheita associada com o amadurecimento
Spin-orbit mode transfer via a classical analog of quantum teleportation
We translate the quantum teleportation protocol into a sequence of coherent
operations involving three degrees of freedom of a classical laser beam. The
protocol, which we demonstrate experimentally, transfers the polarisation state
of the input beam to the transverse mode of the output beam. The role of
quantum entanglement is played by a non-separable mode describing the path and
transverse degrees of freedom. Our protocol illustrates the possibility of new
optical applications based on this intriguing classical analogue of quantum
entanglement.Comment: 5 pages, 7 figure
The graphene sheet versus the 2DEG: a relativistic Fano spin-filter via STM and AFM tips
We explore theoretically the density of states (LDOS) probed by an STM tip of
2D systems hosting an adatom and a subsurface impurity,both capacitively
coupled to AFM tips and traversed by antiparallel magnetic fields. Two kinds of
setups are analyzed, a monolayer of graphene and a two-dimensional electron gas
(2DEG). The AFM tips set the impurity levels at the Fermi energy, where two
contrasting behaviors emerge: the Fano factor for the graphene diverges, while
in the 2DEG it approaches zero. As result, the spin-degeneracy of the LDOS is
lifted exclusively in the graphene system, in particular for the asymmetric
regime of Fano interference. The aftermath of this limit is a counterintuitive
phenomenon, which consists of a dominant Fano factor due to the subsurface
impurity even with a stronger STM-adatom coupling. Thus we find a full
polarized conductance, achievable just by displacing vertically the position of
the STM tip. To the best knowledge, our work is the first to propose the Fano
effect as the mechanism to filter spins in graphene. This feature arises from
the massless Dirac electrons within the band structure and allows us to employ
the graphene host as a relativistic Fano spin-filter
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