669 research outputs found
Evidence for magnetoplasmon character of the cyclotron resonance response of a two-dimensional electron gas
Experimental results on the absolute magneto-transmission of a series of high
density, high mobility GaAs quantum wells are compared with the predictions of
a recent magnetoplasmon theory for values of the filling factor above 2. We
show that the magnetoplasmon picture can explain the non-linear features
observed in the magnetic field evolution of the cyclotron resonance energies
and of the absorption oscillator strength. This provides experimental evidence
that inter Landau level excitations probed by infrared spectroscopy need to be
considered as many body excitations in terms of magnetoplasmons: this is
especially true when interpreting the oscillator strengths of the cyclotron
transitions
Spin relaxation and anticrossing in quantum dots: Rashba versus Dresselhaus spin-orbit coupling
The spin-orbit splitting of the electron levels in a two-dimensional quantum
dot in a perpendicular magnetic field is studied. It is shown that at the point
of an accidental degeneracy of the two lowest levels above the ground state the
Rashba spin-orbit coupling leads to a level anticrossing and to mixing of
spin-up and spin-down states, whereas there is no mixing of these levels due to
the Dresselhaus term. We calculate the relaxation and decoherence times of the
three lowest levels due to phonons. We find that the spin relaxation rate as a
function of a magnetic field exhibits a cusp-like structure for Rashba but not
for Dresselhaus spin-orbit interaction.Comment: 6 pages, 1 figur
Enhancement of the spin-gap in fully occupied two-dimensional Landau levels
Polarization-resolved magneto-luminescence, together with simultaneous
magneto-transport measurements, have been performed on a two-dimensional
electron gas (2DEG) confined in CdTe quantum well in order to determine the
spin-splitting of fully occupied electronic Landau levels, as a function of the
magnetic field (arbitrary Landau level filling factors) and temperature. The
spin splitting, extracted from the energy separation of the \sigma+ and \sigma-
transitions, is composed of the ordinary Zeeman term and a many-body
contribution which is shown to be driven by the spin-polarization of the 2DEG.
It is argued that both these contributions result in a simple, rigid shift of
Landau level ladders with opposite spins.Comment: 4 pages, 3 figure
Low temperature mixed spin state of Co3+ in LaCoO3 evidenced from Jahn-Teller lattice distortions
One- and multi-phonon excitations of the single crystalline LaCoO3 were
studied using Raman spectroscopy in the temperature region of 5 K - 300 K.
First-order Raman spectra show a larger number of phonon modes than allowed for
the rhombohedral structure. Additional phonon modes are interpreted in terms of
activated modes due to lattice distortions, arising from the Jahn-Teller (JT)
activity of the intermediate-spin (IS) state of Co3+ ions. In particular, the
608-cm-1 stretching-type mode shows anomalous behavior in peak energy and
scattering intensity as a function of temperature. The anomalous temperature
dependence of the second-order phonon excitations spectra is in accordance with
the Franck-Condon mechanism that is characteristic for a JT orbital order.Comment: 11 pages, 9 figures, to be published in J. Low. Temp. Physic
Analysis of flame acceleration induced by wall friction in open tubes
Spontaneous flame acceleration leading to explosion triggering in open tubes/channels due to wall friction was analytically and computationally studied. It was first demonstrated that the acceleration is affected when the thermal expansion across the flame exceeds a critical value depending on the combustion configuration. For the axisymmetric flame propagation in cylindrical tubes with both ends open, a theory of the initial (exponential) stage of flame acceleration in the quasi-isobaric limit was developed and substantiated by extensive numerical simulation of the hydrodynamics and combustion with an Arrhenius reaction. The dynamics of the flame shape, velocity, and acceleration rate, as well as the velocity profile ahead and behind the flame, have been determined. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3425646
Extra Spin-Wave mode in Quantum Hall systems. Beyond the Skyrmion Limit
We report on the observation of a new spin mode in a quantum Hall system in
the vicinity of odd electron filling factors under experimental conditions
excluding the possibility of Skyrmion excitations. The new mode having
presumably zero energy at odd filling factors emerges at small deviations from
odd filling factors and couples to the spin-exciton. The existence of an extra
spin mode assumes a nontrivial magnetic order at partial fillings of Landau
levels surrounding quantum Hall ferromagnets other then the Skyrmion crystal.Comment: 9 pages, 4 figure
Development of High Granulated Straw Chambers of Large Sizes
We have developed the baseline design for the straw drift tube tracking
detectors for high rate environment application. The low-mass inner straw
elements and the technology of the multianode straws assembly was devised and
checked. The prototype chamber was constructed and studied the granularity of
similar chambers can be reduced to one cm2.
Submitted to Physics of Elementary Particles and Atomic Nuclei, LettersComment: 6 pages, 10 figure
Observation of Spin Relaxation Anisotropy in Semiconductor Quantum Wells
Spin relaxation of two-dimensional electrons in asymmetrical (001) AlGaAs
quantum wells are measured by means of Hanle effect. Three different spin
relaxation times for spins oriented along [110], [1-10] and [001]
crystallographic directions are extracted demonstrating anisotropy of
D'yakonov-Perel' spin relaxation mechanism. The relative strengths of Rashba
and Dresselhaus terms describing the spin-orbit coupling in semiconductor
quantum well structures. It is shown that the Rashba spin-orbit splitting is
about four times stronger than the Dresselhaus splitting in the studied
structure.Comment: 4 pages, 3 figure
Anomalous Hall effect in a two-dimensional electron gas with spin-orbit interaction
We discuss the mechanism of anomalous Hall effect related to the contribution
of electron states below the Fermi surface (induced by the Berry phase in
momentum space). Our main calculations are made within a model of
two-dimensional electron gas with spin-orbit interaction of the Rashba type,
taking into account the scattering from impurities. We demonstrate that such an
"intrinsic" mechanism can dominate but there is a competition with the
impurity-scattering mechanism, related to the contribution of states in the
vicinity of Fermi surface. We also show that the contribution to the Hall
conductivity from electron states close to the Fermi surface has the intrinsic
properties as well.Comment: 9 pages, 6 figure
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