2,662 research outputs found
Novel metallic and insulating states at a bent quantum Hall junction
A non-planar geometry for the quantum Hall (QH) effect is studied, whereby
two quantum Hall (QH) systems are joined at a sharp right angle. When both
facets are at equal filling factor nu the junction hosts a channel with
non-quantized conductance, dependent on nu. The state is metallic at nu = 1/3,
with conductance along the junction increasing as the temperature T drops. At
nu = 1, 2 it is strongly insulating, and at nu = 3, 4 shows only weak T
dependence. Upon applying a dc voltage bias along the junction, the
differential conductance again shows three different behaviors. Hartree
calculations of the dispersion at the junction illustrate possible
explanations, and differences from planar QH structures are highlighted.Comment: 5 pages, 4 figures, text + figs revised for clarit
Measuring carrier density in parallel conduction layers of quantum Hall systems
An experimental analysis for two parallel conducting layers determines the
full resistivity tensor of the parallel layer, at magnetic fields where the
other layer is in the quantum Hall regime. In heterostructures which exhibit
parallel conduction in the modulation-doped layer, this analysis quantitatively
determines the charge density in the doping layer and can be used to estimate
the mobility. To illustrate one application, experimental data show magnetic
freeze-out of parallel conduction in a modulation doped heterojunction. As
another example, the carrier density of a minimally populated second subband in
a two-subband quantum well is determined. A simple formula is derived that can
estimate the carrier density in a highly resistive parallel layer from a single
Hall measurement of the total system.Comment: 7 pages, 7 figure
A Threat to New Zealand\u27s Tuatara Heats Up
No matter how many times we head to one of New Zealand\u27s offshore islands, the feelings are always a mix of sheer awe at the beauty and biodiversity preserved in these special refuges and lingering nerves. Did we remember all the gear? Do we have enough food and water in case we get stuck? Can the helicopter land on the side of a cliff in these winds? These epic journeys are in pursuit of a lone remnant of the reptile evolutionary tree, with a unique ecology that has big implications under climate change
Among Lions: The Definitive Account of the 1967 Battle for Jerusalem, The Politics of Pressure: American Arms and Israeli Policy Since the Six Day War
Quantum Hall Effect in a Two-Dimensional Electron System Bent by 90 Degrees
Using a new MBE growth technique, we fabricate a two-dimensional electron
system which is bent around an atomically sharp 90 degree corner. In the
quantum Hall regime under tilted magnetic fields, we can measure equilibration
between both co- and counter-propagating edge channels of arbitrary filling
factor ratio. We present here 4-point magnetotransport characterization of the
corner junction with filling factor combinations which can all be explained
using the standard Landauer-Buttiker edge channel picture. The success of this
description confirms the realization of a new type of quantum Hall edge
geometry.Comment: 4 pages, figures included Typographical errors corrected, reference
adde
Technical Note: New methodology for measuring viscosities in small volumes characteristic of environmental chamber particle samples
Herein, a method for the determination of viscosities of small sample volumes is introduced, with important implications for the viscosity determination of particle samples from environmental chambers (used to simulate atmospheric conditions). The amount of sample needed is < 1 μl, and the technique is capable of determining viscosities (η) ranging between 10<sup>−3</sup> and 10<sup>3</sup> Pascal seconds (Pa s) in samples that cover a range of chemical properties and with real-time relative humidity and temperature control; hence, the technique should be well-suited for determining the viscosities, under atmospherically relevant conditions, of particles collected from environmental chambers. In this technique, supermicron particles are first deposited on an inert hydrophobic substrate. Then, insoluble beads (~1 μm in diameter) are embedded in the particles. Next, a flow of gas is introduced over the particles, which generates a shear stress on the particle surfaces. The sample responds to this shear stress by generating internal circulations, which are quantified with an optical microscope by monitoring the movement of the beads. The rate of internal circulation is shown to be a function of particle viscosity but independent of the particle material for a wide range of organic and organic-water samples. A calibration curve is constructed from the experimental data that relates the rate of internal circulation to particle viscosity, and this calibration curve is successfully used to predict viscosities in multicomponent organic mixtures
Fermi liquid to Luttinger liquid transition at the edge of a two-dimensional electron gas
We present experimental results on the tunneling into the edge of a two
dimensional electron gas (2DEG) obtained with a GaAs/AlGaAs cleaved edge
overgrown structure in a strong perpendicular magnetic field. While the 2DEG
exhibits typical fractional quantum Hall features of a very high mobility
sample, we observe the onset of a non-linear current-voltage characteristic in
the vicinity of nu=1. For filling factor nu<1 the system is consistent with a
non-Fermi liquid behavior, such as a Luttinger liquid, whereas for nu>1 we
observe an Ohmic tunneling resistance between the edge and a three dimensional
contact, typical for a Fermi liquid. Hence, at the edge, there is a transition
from a Luttinger liquid to a Fermi liquid. Finally, we show that the Luttinger
liquid exponent at a given filling factor is not universal but depends on
sample parameters.Comment: 4 pages, 4 figure
Single-valley high-mobility (110) AlAs quantum wells with anisotropic mass
We studied a doping series of (110)-oriented AlAs quantum wells (QWs) and
observed transport evidence of single anisotropic-mass valley occupancy for the
electrons in a 150 \AA wide QW. Our calculations of strain and quantum
confinement for these samples predict single anisotropic-mass valley occupancy
for well widths greater than 53 \AA. Below this, double-valley occupation
is predicted such that the longitudinal mass axes are collinear. We observed
mobility anisotropy in the electronic transport along the crystallographic
directions in the ratio of 2.8, attributed to the mass anisotropy as well as
anisotropic scattering of the electrons in the X-valley of AlAs
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