367 research outputs found
Goldstone Mode Relaxation in a Quantum Hall Ferromagnet due to Hyperfine Interaction with Nuclei
Spin relaxation in quantum Hall ferromagnet regimes is studied. As the
initial non-equilibrium state, a coherent deviation of the spin system from the
direction is considered and the breakdown of this Goldstone-mode
state due to hyperfine coupling to nuclei is analyzed. The relaxation occurring
non-exponentially with time is studied in terms of annihilation processes in
the "Goldstone condensate" formed by "zero spin excitons". The relaxation rate
is calculated analytically even if the initial deviation is not small. This
relaxation channel competes with the relaxation mechanisms due to spin-orbit
coupling, and at strong magnetic fields it becomes dominating.Comment: 8 page
Double-exciton component of the cyclotron spin-flip mode in a quantum Hall ferromagnet
We report on the calculation of the cyclotron spin-flip excitation (CSFE) in
a spin-polarized quantum Hall system at unit filling. This mode has a
double-exciton component which contributes to the CSFE correlation energy but
can not be found by means of a mean field approach. The result is compared with
available experimental data.Comment: 9 pages, 2 figure
Development of a low cost robot system for autonomous measuring of spatial field distributions
A new kind of a modular multi-purpose robot system is developed to measure
the spatial field distributions of very large as well as of small and crowded
areas. The probe is automatically placed at a number of pre-defined positions
where measurements are carried out. The advantages of this system are its
very low influence on the measured field as well as its wide area of possible
applications. In addition, the initial costs are quite low. In this paper the
theory underlying the measurement principle is explained. The accuracy is
analyzed and sample measurements are presented
Activation Energy in a Quantum Hall Ferromagnet and Non-Hartree-Fock Skyrmions
The energy of Skyrmions is calculated with the help of a technique based on
the excitonic representation: the basic set of one-exciton states is used for
the perturbation-theory formalism instead of the basic set of one-particle
states. We use the approach, at which a skyrmion-type excitation (at zero Lande
factor) is considered as a smooth non-uniform rotation in the 3D spin space.
The result within the framework of an excitonically diagonalized part of the
Coulomb Hamiltonian can be obtained by any ratio [where is the typical Coulomb
energy ( being the magnetic length); is the cyclotron
frequency], and the Landau-level mixing is thereby taken into account. In
parallel with this, the result is also found exactly, to second order in terms
of the (if supposing to be small) with use of the
total Hamiltonian. When extrapolated to the region , our
calculations show that the skyrmion gap becomes substantially reduced in
comparison with the Hartree-Fock calculations. This fact brings the theory
essentially closer to the available experimental data.Comment: 14 pages, 1 figure. to appear in Phys. Rev. B, Vol. 65 (Numbers ~
19-22), 200
EMC studies on systems with hybrid filter circuits for modern aircraft applications
In this contribution, a new approach for EMC-filter design is presented. Due
to the increasing electrification of modern aircraft, as a result of the More
Electric Aircraft concept, new strategies and approaches are required to
fulfill the strict EMC aircraft standards (DO-160/ED-14 – Sec. 20).
Consequently the weight and volume of the used filter components can be
reduced. A promising approach could be a combination of passive and active
filters. For the same attenuation effect, so-called hybrid filters achieve
either savings in weight and volume, or can obtain an additional filtering
effect with minimal weight increase of an existing system. In this paper, the
underlying theory is explained in detail, carried out in a simulation tool
and the gained insight is demonstrated with a sample measurement
The Cyclotron Spin-Flip Mode as the Lowest-Energy Excitation of Unpolarized Integer Quantum Hall States
The cyclotron spin-flip modes of spin unpolarized integer quantum Hall states
() have been studied with inelastic light scattering. The energy of
these modes is significantly smaller compared to the bare cyclotron gap. Second
order exchange corrections are held responsible for a negative energy
contribution and render these modes the lowest energy excitations of
unpolarized integer quantum Hall states.Comment: Published: Phys. Rev. B 72, 073304 (2005
Simplified modeling of EM field coupling to complex cable bundles
In this contribution, the procedure "Equivalent Cable Bundle Method" is
used for the simplification of large cable bundles, and it is extended to the
application on differential signal lines. The main focus is on the reduction
of twisted-pair cables. Furthermore, the process presented here allows to
take into account cables with wires that are situated quite close to each
other. The procedure is based on a new approach to calculate the geometry of
the simplified cable and uses the fact that the line parameters do not
uniquely correspond to a certain geometry. For this reason, an optimization
algorithm is applied
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