305 research outputs found
Spin dynamics of electrons in the first excited subband of a high-mobility low-density 2D electron system
We report on time-resolved Kerr rotation measurements of spin coherence of
electrons in the first excited subband of a high-mobility low-density
two-dimensional electron system in a GaAs/Al0.35Ga0.65As heterostructure. While
the transverse spin lifetime (T2*) of electrons decreases monotonically with
increasing magnetic field, it has a non-monotonic dependence on the
temperature, with a peak value of 596 ps at 36 K, indicating the effect of
inter-subband electron-electron scattering on the electron spin relaxation. The
spin lifetime may be long enough for potential device application with
electrons in excited subbands
How branching can change the conductance of ballistic semiconductor devices
We demonstrate that branching of the electron flow in semiconductor
nanostructures can strongly affect macroscopic transport quantities and can
significantly change their dependence on external parameters compared to the
ideal ballistic case even when the system size is much smaller than the mean
free path. In a corner-shaped ballistic device based on a GaAs/AlGaAs
two-dimensional electron gas we observe a splitting of the commensurability
peaks in the magnetoresistance curve. We show that a model which includes a
random disorder potential of the two-dimensional electron gas can account for
the random splitting of the peaks that result from the collimation of the
electron beam. The shape of the splitting depends on the particular realization
of the disorder potential. At the same time magnetic focusing peaks are largely
unaffected by the disorder potential.Comment: accepted for publication in Phys. Rev.
Effect of electron-electron scattering on spin dephasing in a high-mobility low-density twodimensional electron gas
Utilizing time-resolved Kerr rotation techniques, we have investigated the
spin dynamics of a high mobility, low density two dimensional electron gas in a
GaAs/Al0:35Ga0:65As heterostructure in dependence on temperature from 1.5 K to
30 K. It is found that the spin relaxation/dephasing time under a magnetic
field of 0.5 T exhibits a maximum of 3.12 ns around 14 K, superimposed on an
increasing background with rising temperature. The appearance of the maximum is
ascribed to that at the temperature where the crossover from the degenerate to
the nondegenerate regime takes place, electron-electron Coulomb scattering
becomes strongest, and thus inhomogeneous precession broadening due to
D'yakonov-Perel'(DP) mechanism becomes weakest. These results agree with the
recent theoretical predictions [Zhou et al., PRB 75, 045305 (2007)], verifying
the importance of electron-electron Coulomb scattering to electron spin
relaxation/dephasing.Comment: 4 pages, 2 figure
Circular polarization dependent study of the microwave photoconductivity in a two-dimensional electron system
The polarization dependence of the low field microwave photoconductivity and
absorption of a two-dimensional electron system has been investigated in a
quasi-optical setup in which linear and any circular polarization can be
produced in-situ. The microwave induced resistance oscillations and the zero
resistance regions are notedly immune to the sense of circular polarization.
This observation is discrepant with a number of proposed theories. Deviations
only occur near the cyclotron resonance absorption where an unprecedented large
resistance response is observed.Comment: 5 pages, 3 figure
Recommendations for myeloid-derived suppressor cell nomenclature and characterization standards
Myeloid-derived suppressor cells (MDSCs) have emerged as major regulators of immune responses in cancer and other pathological conditions. In recent years, ample evidence supports key contributions of MDSC to tumour progression through both immune-mediated mechanisms and those not directly associated with immune suppression. MDSC are the subject of intensive research with >500 papers published in 2015 alone. However, the phenotypic, morphological and functional heterogeneity of these cells generates confusion in investigation and analysis of their roles in inflammatory responses. The purpose of this communication is to suggest characterization standards in the burgeoning field of MDSC research
Controlled Dephasing of Electrons by Non-Gaussian Shot Noise
In a 'controlled dephasing' experiment [1-3], an interferometer loses its
coherence due to entanglement with a controlled quantum system ('which path'
detector). In experiments that were conducted thus far in mesoscopic systems
only partial dephasing was achieved. This was due to weak interactions between
many detector electrons and the interfering electron, resulting in a Gaussian
phase randomizing process [4-10]. Here, we report the opposite extreme: a
complete destruction of the interference via strong phase randomization only by
a few electrons in the detector. The realization was based on interfering edge
channels (in the integer quantum Hall effect regime, filling factor 2) in a
Mach-Zehnder electronic interferometer, with an inner edge channel serving as a
detector. Unexpectedly, the visibility quenched in a periodic lobe-type form as
the detector current increased; namely, it periodically decreased as the
detector current, and thus the detector's efficiency, increased. Moreover, the
visibility had a V-shape dependence on the partitioning of the detector
current, and not the expected dependence on the second moment of the shot
noise, T(1-T), with T the partitioning. We ascribe these unexpected features to
the strong detector-interferometer coupling, allowing only 1-3 electrons in the
detector to fully dephase the interfering electron. Consequently, in this work
we explored the non-Gaussian nature of noise [11], namely, the direct effect of
the shot noise full counting statistics [12-15].Comment: 14 pages, 4 figure
Anisotropy and periodicity in the density distribution of electrons in a quantum-well
We use low temperature near-field optical spectroscopy to image the electron
density distribution in the plane of a high mobility GaAs quantum well. We find
that the electrons are not randomly distributed in the plane, but rather form
narrow stripes (width smaller than 150 nm) of higher electron density. The
stripes are oriented along the [1-10 ] crystal direction, and are arranged in a
quasi-periodic structure. We show that elongated structural mounds, which are
intrinsic to molecular beam epitaxy, are responsible for the creation of this
electron density texture.Comment: 10 pages, 3 figure
The Evolution of Quasiparticle Charge in the Fractional Quantum Hall Regime
The charge of quasiparticles in a fractional quantum Hall (FQH) liquid,
tunneling through a partly reflecting constriction with transmission t, was
determined via shot noise measurements. In the nu=1/3 FQH state, a charge
smoothly evolving from e*=e/3 for t=1 to e*=e for t<<1 was determined, agreeing
with chiral Luttinger liquid theory. In the nu=2/5 FQH state the quasiparticle
charge evolves smoothly from e*=e/5 at t=1 to a maximum charge less than e*=e/3
at t<<1. Thus it appears that quasiparticles with an approximate charge e/5
pass a barrier they see as almost opaque.Comment: 4 pages, Correct figure 3 and caption include
Quasiclassical negative magnetoresistance of a 2D electron gas: interplay of strong scatterers and smooth disorder
We study the quasiclassical magnetotransport of non-interacting fermions in
two dimensions moving in a random array of strong scatterers (antidots,
impurities or defects) on the background of a smooth random potential. We
demonstrate that the combination of the two types of disorder induces a novel
mechanism leading to a strong negative magnetoresistance, followed by the
saturation of the magnetoresistivity at a value determined
solely by the smooth disorder. Experimental relevance to the transport in
semiconductor heterostructures is discussed.Comment: 4 pages, 2 figure
Quasiclassical magnetotransport in a random array of antidots
We study theoretically the magnetoresistance of a
two-dimensional electron gas scattered by a random ensemble of impenetrable
discs in the presence of a long-range correlated random potential. We believe
that this model describes a high-mobility semiconductor heterostructure with a
random array of antidots. We show that the interplay of scattering by the two
types of disorder generates new behavior of which is absent for
only one kind of disorder. We demonstrate that even a weak long-range disorder
becomes important with increasing . In particular, although
vanishes in the limit of large when only one type of disorder is present,
we show that it keeps growing with increasing in the antidot array in the
presence of smooth disorder. The reversal of the behavior of is
due to a mutual destruction of the quasiclassical localization induced by a
strong magnetic field: specifically, the adiabatic localization in the
long-range Gaussian disorder is washed out by the scattering on hard discs,
whereas the adiabatic drift and related percolation of cyclotron orbits
destroys the localization in the dilute system of hard discs. For intermediate
magnetic fields in a dilute antidot array, we show the existence of a strong
negative magnetoresistance, which leads to a nonmonotonic dependence of
.Comment: 21 pages, 13 figure
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