135 research outputs found
Interaction and disorder in bilayer counterflow transport at filling factor one
We study high mobility, interacting GaAs bilayer hole systems exhibiting
counterflow superfluid transport at total filling factor . As the
density of the two layers is reduced, making the bilayer more interacting, the
counterflow Hall resistivity () decreases at a given temperature,
while the counterflow longitudinal resistivity (), which is much
larger than , hardly depends on density. On the other hand, a small
imbalance in the layer densities can result in significant changes in
at , while remains vanishingly small. Our data
suggest that the finite at is a result of mobile vortices
in the superfluid created by the ubiquitous disorder in this system.Comment: 4 pages, 3 figure
Counterflow measurements in strongly correlated GaAs hole bilayers: evidence for electron-hole pairing
We study interacting GaAs bilayer hole systems, with very small interlayer
tunneling, in a counterflow geometry where equal currents are passed in
opposite directions in the two, independently contacted layers. At low
temperatures, both the longitudinal and Hall counterflow resistances tend to
vanish in the quantum Hall state at total bilayer filling ,
demonstrating the pairing of oppositely charged carriers in opposite layers.
The temperature dependence of the counterflow Hall resistance is anomalous
compared to the other transport coefficients: even at relatively high
temperatures (600mK), it develops a very deep minimum, with a value that
is about an order of magnitude smaller than the longitudinal counterflow
resistivity.Comment: 4+ pages, 4 figure
Resistance Spikes at Transitions between Quantum Hall Ferromagnets
We report a new manifestation of first-order magnetic transitions in
two-dimensional electron systems. This phenomenon occurs in aluminum arsenide
quantum wells with sufficiently low carrier densities and appears as a set of
hysteretic spikes in the resistance of a sample placed in crossed parallel and
perpendicular magnetic fields, each spike occurring at the transition between
states with different partial magnetizations. Our experiments thus indicate
that the presence of magnetic domains at the transition starkly increases
dissipation, an effect also suspected in other ferromagnetic materials.
Analysis of the positions of the transition spikes allows us to deduce the
change in exchange-correlation energy across the magnetic transition, which in
turn will help improve our understanding of metallic ferromagnetism.Comment: 6 pages, 3 figure
Role of finite layer thickness in spin-polarization of GaAs 2D electrons in strong parallel magnetic fields
We report measurements and calculations of the spin-polarization, induced by
a parallel magnetic field, of interacting, dilute, two-dimensional electron
systems confined to GaAs/AlGaAs heterostructures. The results reveal the
crucial role the non-zero electron layer thickness plays: it causes a
deformation of the energy surface in the presence of a parallel field, leading
to enhanced values for the effective mass and g-factor and a non-linear
spin-polarization with field.Comment: 4 pages, 4 figures, Fig. 4 has been replaced from the previous
version, minor changes in the tex
Effective mass suppression upon complete spin-polarization in an isotropic two-dimensional electron system
We measure the effective mass (m*) of interacting two-dimensional electrons
confined to a 4.5 nm-wide AlAs quantum well. The electrons in this well occupy
a single out-of-plane conduction band valley with an isotropic in-plane Fermi
contour. When the electrons are partially spin polarized, m* is larger than its
band value and increases as the density is reduced. However, as the system is
driven to full spin-polarization via the application of a strong parallel
magnetic field, m* is suppressed down to values near or even below the band
mass. Our results are consistent with the previously reported measurements on
wide AlAs quantum wells where the electrons occupy an in-plane valley with an
anisotropic Fermi contour and effective mass, and suggest that the effective
mass suppression upon complete spin polarization is a genuine property of
interacting two-dimensional electrons.Comment: 6 pages, 7 figures, accepted for publication in Phys. Rev.
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