1,335 research outputs found
Hanbury Brown and Twiss Correlations of Anderson Localized Waves
When light waves propagate through disordered photonic lattices, they can
eventually become localized due to multiple scattering effects. Here we show
experimentally that while the evolution and localization of the photon density
distribution is similar in the two cases of diagonal and off-diagonal disorder,
the density-density correlation carries a distinct signature of the type of
disorder. We show that these differences reflect a symmetry in the spectrum and
eigenmodes that exists in off-diagonally disordered lattices but is absent in
lattices with diagonal disorder.Comment: 4 pages, 3 figures, comments welcom
Probing Spin-Polarized Currents in the Quantum Hall Regime
An experiment to probe spin-polarized currents in the quantum Hall regime is
suggested that takes advantage of the large Zeeman-splitting in the
paramagnetic diluted magnetic semiconductor zinc manganese selenide
(ZnMnSe). In the proposed experiment spin-polarized electrons are
injected by ZnMnSe-contacts into a gallium arsenide (GaAs) two-dimensional
electron gas (2DEG) arranged in a Hall bar geometry. We calculated the
resulting Hall resistance for this experimental setup within the framework of
the Landauer-B\"uttiker formalism. These calculations predict for 100%
spininjection through the ZnMnSe-contacts a Hall resistance twice as high as in
the case of no spin-polarized injection of charge carriers into a 2DEG for
filling factor . We also investigated the influence of the equilibration
of the spin-polarized electrons within the 2DEG on the Hall resistance. In
addition, in our model we expect no coupling between the contact and the 2DEG
for odd filling factors of the 2DEG for 100% spininjection, because of the
opposite sign of the g-factors of ZnMnSe and GaAs.Comment: 7 pages, 5 figure
Separately contacted edge states: A new spectroscopic tool for the investigation of the quantum Hall effect
Using an innovative combination of a quasi-Corbino sample geometry and the
cross-gate technique, we have developed a method that enables us to separately
contact single edge channels in the quantum Hall regime and investigate
equilibration among them. Performing 4-point resistance measurements, we
directly obtain information on the energetic and geometric structure of the
edge region and the equilibration-length for current transport across the
Landau- as well as the spin-gap. Based on an almost free choice in the number
of participating edge channels and their interaction-length a systematic
investigation of the parameter-space becomes possible.Comment: 8 pages, 7 figure
Dynamic Nuclear Polarization in a Quantum Hall Corbino Disk
Electrical polarization of nuclear spins is studied in a Corbino disk under a
breakdown regime of the quantum Hall effect (QHE). Since the edge channels are
completely absent in the Corbino disk, we conclude that the electric current
flowing in the bulk channel of a quantum Hall conductor is relevant to dynamic
nuclear polarization (DNP). A pump and probe measurement demonstrates that DNP
emerges near the critical voltage of the QHE breakdown. The agreement of the
onset voltage of DNP with that of the QHE breakdown indicates that the
underlying origin of DNP is closely related to that of the QHE breakdown.Comment: 3 pages, 4 figure
Spatially resolved spectroscopy of Coma cluster early-type galaxies - II:the minor axis dataset
We present minor axis, off set major axis and one diagonal long slit spectra for 10 E and S0 galaxies of the Coma cluster drawn from a magnitude-limited sample studied before. We derive rotation curves, velocity dispersion profiles and the H-3 and H-4 coefficients of the Hermite decomposition of the line of sight velocity distribution. Moreover, we derive the line index profiles of Mg, Fe and Hbeta line indices and assess their errors. The data will be used to construct dynamical models of the galaxies and study their stellar populations
The Halpha Luminosity Function of the Galaxy Cluster Abell 521 at z = 0.25
We present an optical multicolor-imaging study of the galaxy cluster Abell
521 at , using Suprime-Cam on the Subaru Telescope, covering an area
of arcmin ( Mpc at ). Our imaging data taken with both a narrow-band filter,
(\AA and \AA), and broad-band filters,
, and allow us to find 165 H
emitters. We obtain the H luminosity function (LF) for the cluster
galaxies within 2 Mpc; the Schechter parameters are ,
Mpc, and erg s. Although the faint end slope, , is consistent with
that of the local cluster H LFs, the characteristic luminosity,
, is about 6 times (or mag) brighter. This strong
evolution implies that Abell 521 contains more active star-forming galaxies
than the local clusters, being consistent with the observed Butcher-Oemler
effect. However, the bright of Abell 521 may be, at least in part,
due to the dynamical condition of this cluster.Comment: 21 pages, 7 figures, ApJ, Part 1, in pres
Thermohydrodynamics in Quantum Hall Systems
A theory of thermohydrodynamics in two-dimensional electron systems in
quantizing magnetic fields is developed including a nonlinear transport regime.
Spatio-temporal variations of the electron temperature and the chemical
potential in the local equilibrium are described by the equations of
conservation with the number and thermal-energy flux densities. A model of
these flux densities due to hopping and drift processes is introduced for a
random potential varying slowly compared to both the magnetic length and the
phase coherence length. The flux measured in the standard transport experiment
is derived and is used to define a transport component of the flux density. The
equations of conservation can be written in terms of the transport component
only. As an illustration, the theory is applied to the Ettingshausen effect, in
which a one-dimensional spatial variation of the electron temperature is
produced perpendicular to the current.Comment: 10 pages, 1 figur
Probing the evolution of early-type galaxies using multi-colour number counts and redshift distributions
We investigate pure luminosity evolution models for early-type (elliptical
and S0) galaxies (i.e., no number density change or morphology transition), and
examine whether these models are consistent with observed number counts in the
B, I and K bands and redshift distributions of two samples of faint galaxies
selected in the I and K bands. The models are characterized by the star
formation time scale and the time when galactic wind blows
in addition to several other conventional parameters. We find the single-burst
model (=0.1 Gyr and =0.353 Gyr), which is known to reproduce
the photometric properties of early-type galaxies in clusters, is inconsistent
with redshift distributions of early-type galaxies in the field environment due
to overpredictions of galaxies at z\gsim1.4 even with strong extinction which
is at work until . In order for dust extinction to be more effective,
we change and as free parameters, and find that models
with \tau_{SF}\gsim0.5 Gyr and Gyr can be made consistent with
both the observed redshift distributions and number counts, if we introduce
strong extinction as a peak value). These results suggest that
early-type galaxies in the field environment do not have the same evolutionary
history as described by the single-burst model.Comment: 6 pages including 4 PS figures; accepted for publication in MNRA
Strong, Ultra-narrow Peaks of Longitudinal and Hall Resistances in the Regime of Breakdown of the Quantum Hall Effect
With unusually slow and high-resolution sweeps of magnetic field, strong,
ultra-narrow (width down to ) resistance peaks are observed in
the regime of breakdown of the quantum Hall effect. The peaks are dependent on
the directions and even the history of magnetic field sweeps, indicating the
involvement of a very slow physical process. Such a process and the sharp peaks
are, however, not predicted by existing theories. We also find a clear
connection between the resistance peaks and nuclear spin polarization.Comment: 5 pages with 3 figures. To appear in PR
Electrostatic effects in coupled quantum dot-point contact-single electron transistor devices
We study the operation of a system where quantum dot (QD) and point contact (PC) defined in a two-dimensional electron gas of a high-mobility GaAs/AlGaAs heterostructure are capacitively coupled to each other and to metallic single electron transistor (SET). The charge state of the quantum dot can be probed by the point contact or single electron transistor. These can be used for sensitive detection of terahertz radiation. In this work, we explore an electrostatic model of the system. From the model, we determine the sensitivity of the point contact and the single electron transistor to the charge excitation of the quantum dot. Nearly periodic oscillations of the point contact conductance are observed in the vicinity of pinch-off voltage. They can be attributed to Coulomb blockade effect in a quasi-1D channel because of unintentional formation of small quantum dot. The latter can be a result of fluctuations in GaAs quantum well thickness
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