11,517 research outputs found
Reentrant nu = 1 quantum Hall state in a two-dimensional hole system
We report the observation of a reentrant quantum Hall state at the Landau
level filling factor nu = 1 in a two-dimensional hole system confined to a
35-nm-wide (001) GaAs quantum well. The reentrant behavior is characterized by
a weakening and eventual collapse of the nu = 1 quantum Hall state in the
presence of a parallel magnetic field component B||, followed by a
strengthening and reemergence as B|| is further increased. The robustness of
the nu = 1 quantum Hall state during the transition depends strongly on the
charge distribution symmetry of the quantum well, while the magnitude of B||
needed to invoke the transition increases with the total density of the system
Anomalous Josephson Current in Junctions with Spin-Polarizing Quantum Point Contacts
We consider a ballistic Josephson junction with a quantum point contact in a
two-dimensional electron gas with Rashba spin-orbit coupling. The point contact
acts as a spin filter when embedded in a circuit with normal electrodes. We
show that with an in-plane external magnetic field an anomalous supercurrent
appears even for zero phase difference between the superconducting electrodes.
In addition, the external field induces large critical current asymmetries
between the two flow directions, leading to supercurrent rectifying effects.Comment: 4 pages, 4 figures, to appear in PR
INTEGRAL spectral variability study of the atoll 4U 1820-30: first detection of hard X-ray emission
We study the 4-200 keV spectral and temporal behaviour of the low mass X-ray
binary 4U 1820-30 with INTEGRAL during 2003-2005. This source as been observed
in both the soft (banana) and hard (island) spectral states. A high energy
tail, above 50 keV, in the hard state has been observed for the first time.
This places the source in the category of X-ray bursters showing high-energy
emission. The tail can be modeled as a soft power law component, with the
photon index of ~2.4, on top of thermal Comptonization emission from a plasma
with the electron temperature of kT_e~6 keV and optical depth of \tau~4.
Alternatively, but at a lower goodness of the fit, the hard-state broad band
spectrum can be accounted for by emission from a hybrid, thermal-nonthermal,
plasma. During this monitoring the source spent most of the time in the soft
state, usual for this source, and the >~4 keV spectra are represented by
thermal Comptonization with kT_e~3 keV and \tau~6-7.Comment: 14 pages, 4 figures, accepted for publication by Ap
Demonstration of detuned dual recycling at the Garching 30m laser interferometer
Dual recycling is an advanced optical technique to enhance the
signal-to-noise ratio of laser interferometric gravitational wave detectors in
a limited bandwidth. To optimise the center of this band with respect to
Fourier frequencies of expected gravitational wave signals detuned dual
recycling has to be implemented. We demonstrated detuned dual recycling on a
fully suspended 30m prototype interferometer. A control scheme that allows to
tune the detector to different frequencies will be outlined. Good agreement
between the experimental results and numerical simulations has been achieved.Comment: 9 page
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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