364 research outputs found
Comment on "Spin relaxation in quantum Hall systems"
W. Apel and Yu.A. Bychkov have recently considered the spin relaxation in a
2D quantum Hall system for the filling factor close to unity [PRL v.82, 3324
(1999)]. The authors considered only one spin flip mechanism (direct
spin-phonon coupling) among several possible spin-orbit related ones and came
to the conclusion that the spin relaxation time due to this mechanism is quite
short: around s at B=10 T (for GaAs). This time is much shorter than
the typical time ( s) obtained earlier by D. Frenkel while considering
the spin relaxation of 2D electrons in a quantizing magnetic field without the
Coulomb interaction and for the same spin-phonon coupling. I show that the
authors' conclusion about the value of the spin-flip time is wrong and have
deduced the correct time which is by several orders of magnitude longer. I also
discuss the admixture mechanism of the spin-orbit interaction.Comment: 1 pag
Gate-Controlled Electron Spin Resonance in a GaAs/AlGaAs Heterostructure
The electron spin resonance (ESR) of two-dimensional electrons is
investigated in a gated GaAs/AlGaAs heterostructure. We found that the ESR
resonance frequency can be turned by means of a gate voltage. The front and
back gates of the heterostructure produce opposite g-factor shift, suggesting
that electron g-factor is being electrostatically controlled by shifting the
equilibrium position of the electron wave function from one epitaxial layer to
another with different g-factors
Resistively Detected NMR in Quantum Hall States: Investigation of the anomalous lineshape near
A study of the resistively detected nuclear magnetic resonance (RDNMR)
lineshape in the vicinity of was performed on a high-mobility 2D
electron gas formed in GaAs/AlGaAs. In higher Landau levels, application of an
RF field at the nuclear magnetic resonance frequency coincides with an observed
minimum in the longitudinal resistance, as predicted by the simple hyperfine
interaction picture. Near however, an anomalous dispersive lineshape is
observed where a resistance peak follows the usual minimum. In an effort to
understand the origin of this anomalous peak we have studied the resonance
under various RF and sample conditions. Interestingly, we show that the
lineshape can be completely inverted by simply applying a DC current. We
interpret this as evidence that the minima and maxima in the lineshape
originate from two distinct mechanisms.Comment: 5 pages, 3 figures, EP2DS 17, to be published in Physica
Measurement of Fairness Perceptions in Energy Transition Research: A Factorial Survey Approach
Justice and fairness are increasingly popular concepts in energy research and comprise several justice dimensions, including distributive and procedural justice, related to energy production and consumption. In this paper, we used factorial survey experiments—a method employed in sociological justice research—for energy transition research. In a factorial survey, respondents evaluated one or more situations described by several attributes, which varied in their levels. The experimental setup of factorial surveys is one of its advantages over simple survey items, as based on this, the relative importance of each attribute for justice evaluations can be determined. We employed the method in a study on the perceived fairness of renewable energy expansion projects related to wind energy, solar energy, and biomass in Germany, and considered aspects of procedural and distributive justice. We show that the effects of these justice dimensions can be separated and the heterogeneity in justice evaluations can be explained. Compared to previous studies applying factorial survey experiments to explain the acceptance of renewable energy projects, we employed the method to directly measure justice concerns and asked respondents to evaluate the vignettes in terms of perceived fairness. This is important because acceptance and fairness as well as inequality and injustice are different phenomena.BMBF, 01LA1110C, Ökonomie des Klimawandels - Verbundvorhaben: Effiziente und gerechte Allokation erneuerbarer Energien auf nationaler Ebenel - Efficient and fair allocation of renewable energy production at the national level (EnergyEFFAIR) - Teilvorhaben
Möglichkeiten und Grenzen der landwirtschaftlichen Interpretation von Reliefparametern aus digitalen Geländemodellen für die GPS-gestützte Landwirtschaft
Precision farming needs precise site information with regard to production potential and indications for optimized management. Besides other data sources (e.g. yield mapping, soil maps), elevation information and topographical derivations are not used very often. We studied the usability of RTK-GPS measurements (cm accuracy) for a 50 ha field to (a) derive a digital elevation model (DEM), and (b) to estimate relative yield potential for some parameters derived from the DEM. Results were compared with actual yield and soil map information, using the transferable belief model (TBM). Processing of RTK-GPS data yielded plausible terrain structures and the interpretation of topographical features as yield zones in general was spatially similar to existing data layers. The TBM allowed for spatially explicit visualization of conflicting hypotheses, what helps improving data sources and/or interpretation schemes
Spin Relaxation in a Quantized Hall Regime in Presence of a Disorder
We study the spin relaxation (SR) of a two-dimensional electron gas (2DEG) in
the quantized Hall regime and discuss the role of spatial inhomogeneity effects
on the relaxation. The results are obtained for small filling factors () or when the filling factor is close to an integer. In either case SR times
are essentially determined by a smooth random potential. For small we
predict a "magneto-confinement" resonance manifested in the enhancement of the
SR rate when the Zeeman energy is close to the spacing of confinement sublevels
in the low-energy wing of the disorder-broadened Landau level. In the resonant
region the -dependence of the SR time has a peculiar non-monotonic shape. If
, the SR is going non-exponentially. Under typical conditions
the calculated SR times range from to s.Comment: 10 pages, 1 figure. To appear in JETP Letter
Nuclear Spin Relaxation for Higher Spin
We study the relaxation of a spin I that is weakly coupled to a quantum
mechanical environment. Starting from the microscopic description, we derive a
system of coupled relaxation equations within the adiabatic approximation.
These are valid for arbitrary I and also for a general stationary
non--equilibrium state of the environment. In the case of equilibrium, the
stationary solution of the equations becomes the correct Boltzmannian
equilibrium distribution for given spin I. The relaxation towards the
stationary solution is characterized by a set of relaxation times, the longest
of which can be shorter, by a factor of up to 2I, than the relaxation time in
the corresponding Bloch equations calculated in the standard perturbative way.Comment: 4 pages, Latex, 2 figure
Electron transport in gated InGaAs and InAsP quantum well wires in selectively-grown InP ridge structures
The purpose of this work is to fabricate ribbon-like InGaAs and InAsP wires
embedded in InP ridge structures and investigate their transport properties.
The InP ridge structures that contain the wires are selectively grown by
chemical beam epitaxy (CBE) on pre-patterned InP substrates. To optimize the
growth and micro-fabrication processes for electronic transport, we explore the
Ohmic contact resistance, the electron density, and the mobility as a function
of the wire width using standard transport and Shubnikov-de Haas measurements.
At low temperatures the ridge structures reveal reproducible mesoscopic
conductance fluctuations. We also fabricate ridge structures with submicron
gate electrodes that exhibit non-leaky gating and good pinch-off
characteristics acceptable for device operation. Using such wrap gate
electrodes, we demonstrate that the wires can be split to form quantum dots
evidenced by Coulomb blockade oscillations in transport measurements.Comment: 5 pages, 4 figures, additional references and improved Fig. 4c,
MSS-14 conference, submitted to Physica
Experimental Evidence for a Spin-Polarized Ground State in the \nu=5/2 Fractional Quantum Hall Effect
We study the \nu=5/2 even-denominator fractional quantum Hall effect (FQHE)
over a wide range of magnetic (B) field in a heterojunction insulated gate
field-effect transistor (HIGFET). The electron density can be tuned from n=0 to
7.6 \times 10^{11} cm^{-2} with a peak mobility \mu = 5.5 \times 10^6 cm^2/Vs.
The \nu=5/2 state shows a strong minimum in diagonal resistance and a
developing Hall plateau at magnetic fields as high as 12.6T. The strength of
the energy gap varies smoothly with B-field. We interpret these observations as
strong evidence for a spin-polarized ground state at \nu=5/2.Comment: new references adde
- …