172 research outputs found
Rock Music Induced Damage and Vibration at Nya Ullevi Stadium
Two rock concerts were held in the City of Gothenburg, Sweden at Nya Ullevi soccer stadium the summer of 985. The stadium is founded on driven piles in soft clay. An enthusiastic audience was jumping in time to the songs. Violent vibrations of the suspension wires and in the cantilever roof beams of the structure were observed and damage to the roof and the building itself was detected after the concerts. People on the pitch and inside the stadium building experienced excessive vibrations. Residential buildings 400 m away experienced vibrations. Concerts are at present not permitted at the stadium. The Gothenburg community suffers financially as a result of being unable to arrange concerts such as these. The high vibration level which occurred during some of the songs can be explained by resonance phenomena in the clay deposit. The paper describes the damage to the structure, the experience of people inside and outside the stadium and by the use of calculations arrives at an explanation for the excessive vibrations
Effect of external magnetic field on electron spin dephasing induced by hyperfine interaction in quantum dots
We investigate the influence of an external magnetic field on spin phase
relaxation of single electrons in semiconductor quantum dots induced by the
hyperfine interaction. The basic decay mechanism is attributed to the
dispersion of local effective nuclear fields over the ensemble of quantum dots.
The characteristics of electron spin dephasing is analyzed by taking an average
over the nuclear spin distribution. We find that the dephasing rate can be
estimated as a spin precession frequency caused primarily by the mean value of
the local nuclear magnetic field. Furthermore, it is shown that the hyperfine
interaction does not fully depolarize electron spin. The loss of initial spin
polarization during the dephasing process depends strongly on the external
magnetic field, leading to the possibility of effective suppression of this
mechanism.Comment: 10 pages, 2 figure
Rashba spin orbit interaction in a quantum wire superlattice
In this work we study the effects of a longitudinal periodic potential on a
parabolic quantum wire defined in a two-dimensional electron gas with Rashba
spin-orbit interaction. For an infinite wire superlattice we find, by direct
diagonalization, that the energy gaps are shifted away from the usual Bragg
planes due to the Rashba spin-orbit interaction. Interestingly, our results
show that the location of the band gaps in energy can be controlled via the
strength of the Rashba spin-orbit interaction. We have also calculated the
charge conductance through a periodic potential of a finite length via the
non-equilibrium Green's function method combined with the Landauer formalism.
We find dips in the conductance that correspond well to the energy gaps of the
infinite wire superlattice. From the infinite wire energy dispersion, we derive
an equation relating the location of the conductance dips as a function of the
(gate controllable) Fermi energy to the Rashba spin-orbit coupling strength. We
propose that the strength of the Rashba spin-orbit interaction can be extracted
via a charge conductance measurement.Comment: 9 pages, 9 figure
Spin decay and quantum parallelism
We study the time evolution of a single spin coupled inhomogeneously to a
spin environment. Such a system is realized by a single electron spin bound in
a semiconductor nanostructure and interacting with surrounding nuclear spins.
We find striking dependencies on the type of the initial state of the nuclear
spin system. Simple product states show a profoundly different behavior than
randomly correlated states whose time evolution provides an illustrative
example of quantum parallelism and entanglement in a decoherence phenomenon.Comment: 6 pages, 4 figures included, version to appear in Phys. Rev.
Current-Induced Entanglement of Nuclear Spins in Quantum Dots
We propose an entanglement mechanism of nuclear spins in quantum dots driven
by the electric current accompanied by the spin flip. This situation is
relevant to a leakage current in spin-blocked regions where electrons cannot be
transported unless their spins are flipped. The current gradually increases the
components of larger total spin of nuclei. This correlation among the nuclear
spins markedly enhances the spin-flip rate of electrons and hence the leakage
current. The enhancement of the current is observable when the residence time
of electrons in the quantum dots is shorter than the dephasing time T*_2 of
nuclear spins.Comment: 4 pages, 4 figure
Spin susceptibilities, spin densities and their connection to spin-currents
We calculate the frequency dependent spin susceptibilities for a
two-dimensional electron gas with both Rashba and Dresselhaus spin-orbit
interaction. The resonances of the susceptibilities depends on the relative
values of the Rashba and Dresselhaus spin-orbit constants, which could be
manipulated by gate voltages. We derive exact continuity equations, with source
terms, for the spin density and use those to connect the spin current to the
spin density. In the free electron model the susceptibilities play a central
role in the spin dynamics since both the spin density and the spin current are
proportional to them.Comment: 6 pages, revtex4 styl
Hyperfine-mediated transitions between a Zeeman split doublet in GaAs quantum dots: The role of the internal field
We consider the hyperfine-mediated transition rate between Zeeman split spin
states of the lowest orbital level in a GaAs quantum dot. We separate the
hyperfine Hamiltonian into a part which is diagonal in the orbital states and
another one which mixes different orbitals. The diagonal part gives rise to an
effective (internal) magnetic field which, in addition to an external magnetic
field, determines the Zeeman splitting. Spin-flip transitions in the dots are
induced by the orbital mixing part accompanied by an emission of a phonon. We
evaluate the rate for different regimes of applied magnetic field and
temperature. The rates we find are bigger that the spin-orbit related rates
provided the external magnetic field is sufficiently low.Comment: 8 pages, 3 figure
Charge and spin density response functions of the clean two-dimensional electron gas with Rashba spin-orbit coupling at finite momenta and frequencies
We analytically evaluate charge and spin density response functions of the
clean two-dimensional electron gas with Rashba spin-orbit coupling at finite
momenta and frequencies. On the basis of our exact expressions we discuss the
accuracy of the long-wavelength and the quasiclassical approximations. We also
derive the static limit of spin susceptibilities and demonstrate, in
particular, how the Kohn-like anomalies in their derivatives are related to the
spin-orbit modification of the Ruderman-Kittel-Kasuya-Yosida interaction.
Taking into account screening and exchange effects of the Coulomb interaction,
we describe the collective charge and spin density excitation modes which
appear to be coupled due to nonvanishing spin-charge response function.Comment: 15 pages, 9 figure
Quantum-dot spin qubit and hyperfine interaction
We review our investigation of the spin dynamics for two electrons confined
to a double quantum dot under the influence of the hyperfine interaction
between the electron spins and the surrounding nuclei. Further we propose a
scheme to narrow the distribution of difference in polarization between the two
dots in order to suppress hyperfine induced decoherence.Comment: 12 pages, 3 figures; Presented as plenary talk at the annual DPG
meeting 2006, Dresden (to appear in Advances in Solid State Physics vol. 46,
2006
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