272 research outputs found
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
Negative differential Rashba effect in two-dimensional hole systems
We demonstrate experimentally and theoretically that two-dimensional (2D)
heavy hole systems in single heterostructures exhibit a \emph{decrease} in
spin-orbit interaction-induced spin splitting with an increase in perpendicular
electric field. Using front and back gates, we measure the spin splitting as a
function of applied electric field while keeping the density constant. Our
results are in contrast to the more familiar case of 2D electrons where spin
splitting increases with electric field.Comment: 3 pages, 3 figures. To appear in AP
In-Plane Magnetodrag between Dilute Two-Dimensional Systems
We performed in-plane magnetodrag measurements on dilute double layer
two-dimensional hole systems, at in-plane magnetic fields that suppress the
apparent metallic behavior, and to fields well above those required to fully
spin polarize the system. When compared to the single layer magnetoresistance,
the magnetodrag exhibits exactly the same qualitative behavior. In addition, we
have found that the enhancement to the drag from the in-plane field exhibits a
strong maximum when both layer densities are matched.Comment: 4 pages, 3 figures; minor corrections. Accepted in Phys. Rev. Let
Anisotropic composite fermions and fractional quantum Hall effect
We study the role of anisotropy on the transport properties of composite
fermions near Landau level filling factor in two-dimensional holes
confined to a GaAs quantum well. By applying a parallel magnetic field, we tune
the composite fermion Fermi sea anisotropy and monitor the relative change of
the transport scattering time at along the principal directions.
Interpreted in a simple Drude model, our results suggest that the scattering
time is longer along the longitudinal direction of the composite fermion Fermi
sea. Furthermore, the measured energy gap for the fractional quantum Hall state
at decreases when anisotropy becomes significant. The decrease,
however, might partly stem from the charge distribution becoming bilayer-like
at very large parallel magnetic fields
Reorientation of the stripe Phase of 2D Electrons by a Minute Density Modulation
Interacting two-dimensional electrons confined in a GaAs quantum well exhibit
isotropic transport when the Fermi level resides in the first excited ()
Landau level. Adding an in-plane magnetic field () typically leads to
an anisotropic, stripe-like (nematic) phase of electrons with the stripes
oriented perpendicular to the direction. Our experimental data reveal
how a periodic density modulation, induced by a surface strain grating from
strips of negative electron-beam resist, competes against the -induced
orientational order of the stripe phase. Even a minute () density
modulation is sufficient to reorient the stripes along the direction of the
surface grating.Comment: Accepted for publication in Phys. Rev. Let
Spin susceptibility of two-dimensional electrons in narrow AlAs quantum wells
We report measurements of the spin susceptibility in dilute two-dimensional
electrons confined to a 45 wide AlAs quantum well. The electrons in this
well occupy an out-of-plane conduction-band valley, rendering a system similar
to two-dimensional electrons in Si-MOSFETs but with only one valley occupied.
We observe an enhancement of the spin susceptibility over the band value that
increases as the density is decreased, following closely the prediction of
quantum Monte Carlo calculations and continuing at finite values through the
metal-insulator transition.Comment: 4+ pages, 4 figures. Dotted line added to Fig. 4(a) to clarify the
QMC calculatio
Observation of fractional quantum Hall effect in an InAs quantum well
The two-dimensional electron system in an InAs quantum well has emerged as a
prime candidate for hosting exotic quasi-particles with non-Abelian statistics
such as Majorana fermions and parafermions. To attain its full promise,
however, the electron system has to be clean enough to exhibit
electron-electron interaction phenomena. Here we report the observation of
fractional quantum Hall effect in a very low disorder InAs quantum well with a
well-width of 24 nm, containing a two-dimensional electron system with a
density cm and low-temperature mobility cm/Vs. At a temperature of mK and T, we
observe a deep minimum in the longitudinal resistance, accompanied by a nearly
quantized Hall plateau at Landau level filling factor
Tuning of Fermi Contour Anisotropy in GaAs (001) 2D Holes via Strain
We demonstrate tuning of the Fermi contour anisotropy of two-dimensional (2D)
holes in a symmetric GaAs (001) quantum well via the application of in-plane
strain. The ballistic transport of high-mobility hole carriers allows us to
measure the Fermi wavevector of 2D holes via commensurability oscillations as a
function of strain. Our results show that a small amount of in-plane strain, on
the order of , can induce significant Fermi wavevector anisotropy as
large as 3.3, equivalent to a mass anisotropy of 11 in a parabolic band. Our
method to tune the anisotropy \textit{in situ} provides a platform to study the
role of anisotropy on phenomena such as the fractional quantum Hall effect and
composite fermions in interacting 2D systems.Comment: Accepted to Applied Physics Letter
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