8,394 research outputs found
The dominant spin relaxation mechanism in compound organic semiconductors
Despite the recent interest in "organic spintronics", the dominant spin
relaxation mechanism of electrons or holes in an organic compound semiconductor
has not been conclusively identified. There have been sporadic suggestions that
it might be hyperfine interaction caused by background nuclear spins, but no
confirmatory evidence to support this has ever been presented. Here, we report
the electric-field dependence of the spin diffusion length in an organic
spin-valve structure consisting of an Alq3 spacer layer, and argue that this
data, as well as available data on the temperature dependence of this length,
contradict the notion that hyperfine interactions relax spin. Instead, they
suggest that the Elliott-Yafet mechanism, arising from spin-orbit interaction,
is more likely the dominant spin relaxing mechanism.Comment: Accepted for publication in Physical Review
Displaced Higgs production in type III seesaw
We point out that the type III seesaw mechanism introducing fermion triplets
predicts peculiar Higgs boson signatures of displaced vertices with two b jets
and one or two charged particles which can be cleanly identified. In a
supersymmetric theory, the scalar partner of the fermion triplet contains a
neutral dark matter candidate which is almost degenerate with its charged
components. A Higgs boson can be produced together with such a dark matter
triplet in the cascade decay chain of a strongly produced squark or gluino.
When the next lightest supersymmetric particle (NLSP) is bino/wino-like, there
appears a Higgs boson associated with two charged tracks of a charged lepton
and a heavy charged scalar at a displacement larger than about 1 mm. The
corresponding production cross-section is about 0.5 fb for the squark/gluino
mass of 1 TeV. In the case of the stau NLSP, it decays mainly to a Higgs boson
and a heavy charged scalar whose decay length is larger than 0.1 mm for the
stau NLSP mixing with the left-handed stau smaller than 0.3. As this process
can have a large cascade production pb for the squark/gluino mass
TeV, one may be able to probe it at the early stage of the LHC
experiment.Comment: 10 pages, 5 figure
Entangling capacities of noisy two-qubit Hamiltonians
We show that intrinsic fluctuations in system control parameters impose
limits on the ability of two-qubit (exchange) Hamiltonians to generate
entanglement starting from mixed initial states. We find three classes for
Gaussian and Laplacian fluctuations. For the Ising and XYZ models there are
qualitatively distinct sharp entanglement-generation transitions, while the
class of Heisenberg, XY, and XXZ Hamiltonians is capable of generating
entanglement for any finite noise level. Our findings imply that exchange
Hamiltonians are surprisingly robust in their ability to generate entanglement
in the presence of noise, thus potentially reducing the need for quantum error
correction.Comment: 5 pages, incl. 2 figures. replaced with published versio
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