39,021 research outputs found
Full counting statistics of spin transfer through ultrasmall quantum dots
We analyze the spin-resolved full counting statistics of electron transfer
through an ultrasmall quantum dot coupled to metallic electrodes. Modelling the
setup by the Anderson Hamiltonian, we explicitly take into account the onsite
Coulomb repulsion . We calculate the cumulant generating function for the
probability to transfer a certain number of electrons with a preselected spin
orientation during a fixed time interval. With the cumulant generating function
at hand we are then able to calculate the spin current correlations which are
of outmost importance in the emerging field of spintronics. We confirm the
existing results for the charge statistics and report the discovery of the new
type of correlation between the spin-up and -down polarized electrons flows,
which has a potential to become a powerful new instrument for the investigation
of the Kondo effect in nanostructures.Comment: 5 pages, 1 figur
IPCS implications for future supersonic transport aircraft
The Integrated Propulsion Control System (IPCS) demonstrates control of an entire supersonic propulsion module - inlet, engine afterburner, and nozzle - with an HDC 601 digital computer. The program encompasses the design, build, qualification, and flight testing of control modes, software, and hardware. The flight test vehicle is an F-111E airplane. The L.H. inlet and engine will be operated under control of a digital computer mounted in the weapons bay. A general description and the current status of the IPCS program are given
Shuttle payload S-band communications system
The Shuttle payload S-band communications system design, operational capabilities, and performance are described in detail. System design requirements, overall system and configuration and operation, and laboratory/flight test results are presented. Payload communications requirements development is discussed in terms of evolvement of requirements as well as the resulting technical challenges encountered in meeting the initial requirements. Initial design approaches are described along with cost-saving initiatives that subsequently had to be made. The resulting system implementation that was finally adopted is presented along with a functional description of the system operation. A description of system test results, problems encountered, how the problems were solved, and the system flight experience to date is presented. Finally, a summary of the advancements made and the lessons learned is discussed
Full counting statistics of spin transfer through the Kondo dot
We calculate the spin current distribution function for a Kondo dot in two
different regimes. In the exactly solvable Toulouse limit the linear response,
zero temperature statistics of the spin transfer is trinomial, such that all
the odd moments vanish and the even moments follow a binomial distribution. On
the contrary, the corresponding spin-resolved distribution turns out to be
binomial. The combined spin and charge statistics is also determined. In
particular, we find that in the case of a finite magnetic field or an
asymmetric junction the spin and charge measurements become statistically
dependent. Furthermore, we analyzed the spin counting statistics of a generic
Kondo dot at and around the strong-coupling fixed point (the unitary limit).
Comparing these results with the Toulouse limit calculation we determine which
features of the latter are generic and which ones are artifacts of the spin
symmetry breaking.Comment: 9 pages, 3 eps figure
Electronic and optical properties of quantum wells embedded in wrinkled nanomembranes
The authors theoretically investigate quantum confinement and transition
energies in quantum wells (QWs) asymmetrically positioned in wrinkled
nanomembranes. Calculations reveal that the wrinkle profile induces both blue-
and redshifts depending on the lateral position of the QW probed. Relevant
radiative transistions include the ground state of the electron (hole) and
excited states of the hole (electron). Energy shifts as well as stretchability
of the structure are studied as a function of wrinkle amplitude and period.
Large tunable bandwidths of up to 70 nm are predicted for highly asymmetric
wrinkled QWs.Comment: 3 pages, 4 figures. The following article has been submitted to
Applied Physics Letters. After it is published, it will be found at
http://apl.aip.or
Crystal water induced switching of magnetically active orbitals in CuCl2
The dehydration of CuCl2*2(H2O) to CuCl2 leads to a dramatic change in
magnetic behavior and ground state. Combining density functional electronic
structure and model calculations with thermodynamical measurements we reveal
the microscopic origin of this unexpected incident -- a crystal water driven
switching of the magnetically active orbitals. This switching results in a
fundamental change of the coupling regime from a three-dimensional
antiferromagnet to a quasi one-dimensional behavior. CuCl2 can be well
described as a frustrated J1-J2 Heisenberg chain with ferromagnetic exchange J1
and J2/J1 ~ -1.5 for which a helical ground state is predicted.Comment: 6 pages, 5 figures, 1 table (PRB, accepted
Hanbury-Brown-Twiss correlations and noise in the charge transfer statistics through a multiterminal Kondo dot
We analyze the full counting statistics of charge transfer through a quantum
dot in the Kondo regime, when coupled to an arbitrary number of terminals N.
At the unitary Kondo fixed point and for N>2 we recover distinct
anticorrelations of currents in concurring transport channels, which are
related to the fermionic
Hanbury Brown and Twiss (HBT) antibunching.
This effect weakens as one moves away from the fixed point.
Furthermore, we identify a special class of current correlations that are due
entirely to the virtual polarization of the Kondo singlet.
These can be used for extracting information on the parameters of the
underlying Fermi-liquid model.Comment: 5 page
Bending and wrinkling as competing relaxation pathways for strained free-hanging films
An equilibrium phase diagram for the shape of compressively strained
free-hanging films is developed by total strain energy minimization. For small
strain gradients {\Delta}{\epsilon}, the film wrinkles, while for sufficiently
large {\Delta}{\epsilon}, a phase transition from wrinkling to bending occurs.
We consider competing relaxation mechanisms for free-hanging films, which have
rolled up into tube structures, and we provide an upper limit for the maximum
achievable number of tube rotations.Comment: 4 pages, 4 figure
A new method based on noise counting to monitor the frontend electronics of the LHCb muon detector
A new method has been developed to check the correct behaviour of the
frontend electronics of the LHCb muon detector. This method is based on the
measurement of the electronic noise rate at different thresholds of the
frontend discriminator. The method was used to choose the optimal discriminator
thresholds. A procedure based on this method was implemented in the detector
control system and allowed the detection of a small percentage of frontend
channels which had deteriorated. A Monte Carlo simulation has been performed to
check the validity of the method
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