4,314 research outputs found
Independently contacted two-dimensional electron systems in double quantum wells
A new technique for creating independent ohmic contacts to closely spaced two-dimensional electron systems in double quantum well (DQW) structures is described. Without use of shallow diffusion or precisely controlled etching methods, the present technique results in low-resistance contacts which can be electrostatically switched between the two-conducting layers. The method is demonstrated with a DQW consisting of two 200 Ã… GaAs quantum wells separated by a 175 Ã… AlGaAs barrier. A wide variety of experiments on Coulomb and tunnel-coupled 2D electron systems is now accessible
Field-induced resonant tunneling between parallel two-dimensional electron systems
Resonant tunneling between two high-mobility two-dimensional (2D) electron systems in a double quantum well structure has been induced by the action of an external Schottky gate field. Using one 2D electron gas as source and the other as drain, the tunnel conductance between them shows a strong resonance when the gate field aligns the ground subband edges of the two quantum wells
Forecasting isocurvature models with CMB lensing information: axion and curvaton scenarios
Some inflationary models predict the existence of isocurvature primordial
fluctuations, in addition to the well known adiabatic perturbation. Such mixed
models are not yet ruled out by available data sets. In this paper we explore
the possibility of obtaining better constraints on the isocurva- ture
contribution from future astronomical data. We consider the axion and curvaton
inflationary scenarios, and use Planck satellite experimental specifications
together with SDSS galaxy survey to forecast for the best parameter error
estimation by means of the Fisher information matrix formal- ism. In
particular, we consider how CMB lensing information can improve this forecast.
We found substantial improvements for all the considered cosmological
parameters. In the case of isocurvature amplitude this improvement is strongly
model dependent, varying between less than 1% and above 20% around its fiducial
value. Furthermore, CMB lensing enables the degeneracy break between the
isocurvature amplitude and correlation phase in one of the models. In this
sense, CMB lensing information will be crucial in the analysis of future data.Comment: Accepted for publication in PR
Vanishing Hall Resistance at High Magnetic Field in a Double Layer Two-Dimensional Electron System
At total Landau level filling factor a double layer
two-dimensional electron system with small interlayer separation supports a
collective state possessing spontaneous interlayer phase coherence. This state
exhibits the quantized Hall effect when equal electrical currents flow in
parallel through the two layers. In contrast, if the currents in the two layers
are equal, but oppositely directed, both the longitudinal and Hall resistances
of each layer vanish in the low temperature limit. This finding supports the
prediction that the ground state at is an excitonic superfluid.Comment: 4 pages, 4 figure
Bilayer Quantum Hall Systems at nuT = 1: Coulomb Drag and the Transition from Weak to Strong Interlayer Coupling
Measurements revealing anomalously large frictional drag at the transition between the weakly and strongly coupled regimes of a bilayer two-dimensional electron system at total Landau level filling factor nuT = 1 are reported. This result suggests the existence of fluctuations, either static or dynamic, near the phase boundary separating the quantized Hall state at small layer separations from the compressible state at larger separations. Interestingly, the anomalies in drag seem to persist to larger layer separations than does interlayer phase coherence as detected in tunneling
Charge metastability and hysteresis in the quantum Hall regime
We report simultaneous quasi-dc magnetotransport and high frequency surface
acoustic wave measurements on bilayer two-dimensional electron systems in GaAs.
Near strong integer quantized Hall states a strong magnetic field sweep
hysteresis in the velocity of the acoustic waves is observed at low
temperatures. This hysteresis indicates the presence of a metastable state with
anomalously high conductivity in the interior of the sample. This
non-equilibrium state is not revealed by conventional low frequency transport
measurements which are dominated by dissipationless transport at the edge of
the 2D system. We find that a field-cooling technique allows the equilibrium
charge configuration within the interior of the sample to be established. A
simple model for this behavior is discussed.Comment: 8 pages, 4 postscript figure
Double layer two-dimensional electron systems: Probing the transition from weak to strong coupling with Coulomb drag
Frictional drag measurements revealing anomalously large dissipation at the
transition between the weakly- and strongly-coupled regimes of a bilayer
two-dimensional electron system at total Landau level filling factor
are reported. This result suggests the existence of fluctuations, either static
or dynamic, near the phase boundary separating the quantized Hall state at
small layer separations from the compressible state at larger separations.
Interestingly, the anomalies in drag seem to persist to larger layer
separations than does interlayer phase coherence as detected in tunneling.Comment: 4 pages, 4 figure
A New Statistic for Analyzing Baryon Acoustic Oscillations
We introduce a new statistic omega_l for measuring and analyzing large-scale
structure and particularly the baryon acoustic oscillations. omega_l is a
band-filtered, configuration space statistic that is easily implemented and has
advantages over the traditional power spectrum and correlation function
estimators. Unlike these estimators, omega_l can localize most of the acoustic
information into a single dip at the acoustic scale while also avoiding
sensitivity to the poorly constrained large scale power (i.e., the integral
constraint) through the use of a localized and compensated filter. It is also
sensitive to anisotropic clustering through pair counting and does not require
any binning. We measure the shift in the acoustic peak due to nonlinear effects
using the monopole omega_0 derived from subsampled dark matter catalogues as
well as from mock galaxy catalogues created via halo occupation distribution
(HOD) modeling. All of these are drawn from 44 realizations of 1024^3 particle
dark matter simulations in a 1h^{-1}Gpc box at z=1. We compare these shifts
with those obtained from the power spectrum and conclude that the results
agree. This indicates that any distance measurements obtained from omega_0 and
P(k) will be consistent with each other. We also show that it is possible to
extract the same amount of acoustic information using either omega_0 or P(k)
from equal volume surveys.Comment: 12 pages, 7 figures. ApJ accepted. Edit: Now updated with final
accepted versio
Metastable Resistance Anisotropy Orientation of Two-Dimensional Electrons in High Landau Levels
In half-filled high Landau levels, two-dimensional electron systems possess
collective phases which exhibit a strongly anisotropic resistivity tensor. A
weak, but as yet unknown, rotational symmetry-breaking potential native to the
host semiconductor structure is necessary to orient these phases in macroscopic
samples. Making use of the known external symmetry-breaking effect of an
in-plane magnetic field, we find that the native potential can have two
orthogonal local minima. It is possible to initialize the system in the higher
minimum and then observe its relaxation toward equilibrium.Comment: 5 pages, 3 figures. Figure references corrected. Version accepted for
publication in Physical Review Letter
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