957 research outputs found
Anomalous Quartic and Couplings in Collision With Initial Beams and Final State Polarizations
The constraints on the anomalous quartic and
gauge boson couplings are investigated through the processes
and . Considering the
longitudinal and transverse polarization states of the final W or Z boson and
incoming beam polarizations we find 95% confidence level limits on the
anomalous coupling parameters and with an integrated luminosity
of 500 and =0.5, 1 TeV energies. Assuming the
couplings are independent of the
couplings we show that the longitudinal polarization state of the final gauge
boson improves the sensitivity to anomalous couplings by a factor of 2-3
depending on energy and coupling. An extra enhancement in sensitivity by a
factor of 1.3 comes from a set of initial beam polarizations
Lateral Effects in Fermion Antibunching
Lateral effects are analyzed in the antibunching of a beam of free
non-interacting fermions. The emission of particles from a source is
dynamically described in a 3D full quantum field-theoretical framework. The
size of the source and the detectors, as well as the temperature of the source
are taken into account and the behavior of the visibility is scrutinized as a
function of these parameters.Comment: 22 pages, 4 figure
INDONESIAN HATCHERY REARED SEABASS LARVAE (Lates calcarifer), ASSOCIATED WITH VIRAL NERVOUS NECROSIS (VNN)
Mass tuortality atuongs seabass larvae, Lates calcarifer, reared in hatcheries in East and Bali due to viral nervous necrosis were investigated. outbreaks of the disease occured from August to Novetnber 1997
Spin Diode Based on Fe/MgO Double Tunnel Junction
We demonstrate a spin diode consisting of a semiconductor free nano-scale
Fe/MgO-based double tunnel junction. The device exhibits a near perfect
spin-valve effect combined with a strong diode effect. The mechanism consistent
with our data is resonant tunneling through discrete states in the middle
ferromagnetic layer sandwiched by tunnel barriers of different spin-dependent
transparency. The observed magneto-resistance is record high, ~4000%,
essentially making the structure an on/off spin-switch. This, combined with the
strong diode effect, ~100, offers a new device that should be promising for
such technologies as magnetic random access memory and re-programmable logic.Comment: 14 page
Vertical current induced domain wall motion in MgO-based magnetic tunnel junction with low current densities
Shifting electrically a magnetic domain wall (DW) by the spin transfer
mechanism is one of the future ways foreseen for the switching of spintronic
memories or registers. The classical geometries where the current is injected
in the plane of the magnetic layers suffer from a poor efficiency of the
intrinsic torques acting on the DWs. A way to circumvent this problem is to use
vertical current injection. In that case, theoretical calculations attribute
the microscopic origin of DW displacements to the out-of-plane (field-like)
spin transfer torque. Here we report experiments in which we controllably
displace a DW in the planar electrode of a magnetic tunnel junction by vertical
current injection. Our measurements confirm the major role of the out-of-plane
spin torque for DW motion, and allow to quantify this term precisely. The
involved current densities are about 100 times smaller than the one commonly
observed with in-plane currents. Step by step resistance switching of the
magnetic tunnel junction opens a new way for the realization of spintronic
memristive devices
Observation of band structure and density of states effects in Co-based magnetic tunnel junctions
Utilizing Co/AlO/Co magnetic tunnel junctions (MTJs) with Co
electrodes of different crystalline phases, a clear relationship between
electrode structure and junction transport properties is presented. For
junctions with one fcc(111) textured and one polycrystalline (poly-phase and
poly-directional) Co electrode, a strong asymmetry is observed in the
magnetotransport properties, while when both electrodes are polycrystalline the
magnetotransport is essentially symmetric. These observations are successfully
explained within a model based on ballistic tunneling between the calculated
band structures (DOS) of fcc-Co and hcp-Co.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Quantum Coherence of Electrons Field-Emitted from a Superconductor: Correlations and Entanglement
The correlations of the electrons field-emitted from a superconductor are
fully analyzed, both in space and time. It is proposed that a coincidence
experiment would reveal a positive correlation between the electrons emitted in
opposite directions. The electrons can be entangled and can even violate Bell's
inequality. The crucial role played by Andreev's process is scrutinized,
analytical formulas are derived for the correlations, and the physics behind
the phenomenon is clarified.Comment: 21 pages, 9 figures, typos correcte
Crossover from Kondo assisted suppression to co-tunneling enhancement of tunneling magnetoresistance via ferromagnetic nanodots in MgO tunnel barriers
Recently, it has been shown that magnetic tunnel junctions with thin MgO
tunnel barriers exhibit extraordinarily high tunneling magnetoresistance (TMR)
values at room temperature1, 2. However, the physics of spin dependent
tunneling through MgO barriers is only beginning to be unravelled. Using planar
magnetic tunnel junctions in which ultra-thin layers of magnetic metals are
deposited in the middle of a MgO tunnel barrier here we demonstrate that the
TMR is strongly modified when these layers are discontinuous and composed of
small pancake shaped nanodots. At low temperatures, in the Coulomb blockade
regime, for layers less than ~1 nm thick, the conductance of the junction is
increased at low bias consistent with Kondo assisted tunneling. In the same
regime we observe a suppression of the TMR. For slightly thicker layers, and
correspondingly larger nanodots, the TMR is enhanced at low bias, consistent
with co-tunneling.Comment: Nano Letters (in press
On the Assumption of Initial Factorization in the Master Equation for Weakly Coupled Systems II: Solvable Models
We analyze some solvable models of a quantum mechanical system in interaction
with a reservoir when the initial state is not factorized. We apply
Nakajima-Zwanzig's projection method by choosing a reference state of the
reservoir endowed with the mixing property. In van Hove's limit, the dynamics
is described in terms of a master equation. We observe that Markovianity
becomes a valid approximation for timescales that depend both on the form
factors of the interaction and on the observables of the reservoir that can be
measured.Comment: 25 page
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