854 research outputs found
Specific Heat of a Fractional Quantum Hall System
Using a time-resolved phonon absorption technique, we have measured the
specific heat of a two-dimensional electron system in the fractional quantum
Hall effect regime. For filling factors
and 1/3 the specific heat displays a strong exponential temperature dependence
in agreement with excitations across a quasi-particle gap. At filling factor
we were able to measure the specific heat of a composite fermion
system for the first time. The observed linear temperature dependence on
temperature down to K agrees well with early predictions for a Fermi
liquid of composite fermions.Comment: 4 pages, 4 figures (version is 1. resubmission: Added a paragraph to
include the problems which arise by the weak temperature dependence at \nu =
1/2, updated affiliation
Transport Gap in Suspended Bilayer Graphene at Zero Magnetic Field
We report a change of three orders of magnitudes in the resistance of a
suspended bilayer graphene flake which varies from a few ks in the high
carrier density regime to several Ms around the charge neutrality point
(CNP). The corresponding transport gap is 8 meV at 0.3 K. The sequence of
appearing quantum Hall plateaus at filling factor followed by
suggests that the observed gap is caused by the symmetry breaking of the lowest
Landau level. Investigation of the gap in a tilted magnetic field indicates
that the resistance at the CNP shows a weak linear decrease for increasing
total magnetic field. Those observations are in agreement with a spontaneous
valley splitting at zero magnetic field followed by splitting of the spins
originating from different valleys with increasing magnetic field. Both, the
transport gap and field response point toward spin polarized layer
antiferromagnetic state as a ground state in the bilayer graphene sample. The
observed non-trivial dependence of the gap value on the normal component of
suggests possible exchange mechanisms in the system.Comment: 8 pages, 5 figure
Transport and thermoelectric properties of the LaAlO/SrTiO interface
The transport and thermoelectric properties of the interface between
SrTiO and a 26-monolayer thick LaAlO-layer grown at high
oxygen-pressure have been investigated at temperatures from 4.2 K to 100 K and
in magnetic fields up to 18 T. For 4.2 K, two different electron-like
charge carriers originating from two electron channels which contribute to
transport are observed. We probe the contributions of a degenerate and a
non-degenerate band to the thermoelectric power and develop a consistent model
to describe the temperature dependence of the thermoelectric tensor. Anomalies
in the data point to an additional magnetic field dependent scattering.Comment: 7 pages, 4 figure
Constructive role of non-adiabaticity for quantized charge pumping
We investigate a recently developed scheme for quantized charge pumping based
on single-parameter modulation. The device was realized in an AlGaAl-GaAs gated
nanowire. It has been shown theoretically that non-adiabaticity is
fundamentally required to realize single-parameter pumping, while in previous
multi-parameter pumping schemes it caused unwanted and less controllable
currents. In this paper we demonstrate experimentally the constructive and
destructive role of non-adiabaticity by analysing the pumping current over a
broad frequency range.Comment: Presented at ICPS 2010, July 25 - 30, Seoul, Kore
Thermochronology of the modern Indus River bedload: New insight into the controls on the marine stratigraphic record
The Indus River is the only major drainage in the western Himalaya and delivers a long geological record of continental erosion to the Arabian Sea, which may be deciphered and used to reconstruct orogenic growth if the modern bedload can be related to the mountains. In this study we collected thermochronologic data from river sediment collected near the modern delta. U-Pb ages of zircons spanning 3 Gyr show that only ∼5% of the eroding crust has been generated since India-Asia collision. The Greater Himalaya are the major source of zircons, with additional contributions from the Karakoram and Lesser Himalaya. The 39Ar/40Ar dating of muscovites gives ages that cluster between 10 and 25 Ma, differing from those recorded in the Bengal Fan. Biotite ages are generally younger, ranging 0–15 Ma. Modern average exhumation rates are estimated at ∼0.6 km/m.y. or less, and have slowed progressively since the early Miocene (∼20 Ma), although fission track (FT) dating of apatites may indicate a recent moderate acceleration in rates since the Pliocene (∼1.0 km/m.y.) driven by climate change. The 39Ar/40Ar and FT techniques emphasize the dominance of high topography in controlling the erosional flux to the ocean. Localized regions of tectonically driven, very rapid exhumation (e.g., Nanga Parbat, S. Karakoram metamorphic domes) do not dominate the erosional record
Quantum resistance metrology in graphene
We have performed a metrological characterization of the quantum Hall
resistance in a 1 m wide graphene Hall-bar. The longitudinal resistivity
in the center of the quantum Hall plateaus vanishes within the
measurement noise of 20 m upto 2 A. Our results show that the
quantization of these plateaus is within the experimental uncertainty (15 ppm
for 1.5A current) equal to that in conventional semiconductors. The
principal limitation of the present experiments are the relatively high contact
resistances in the quantum Hall regime, leading to a significantly increased
noise across the voltage contacts and a heating of the sample when a high
current is applied
Room-Temperature Quantum Hall Effect in Graphene
The quantum Hall effect (QHE), one example of a quantum phenomenon that occur
on a truly macroscopic scale, has been attracting intense interest since its
discovery in 1980 and has helped elucidate many important aspects of quantum
physics. It has also led to the establishment of a new metrological standard,
the resistance quantum. Disappointingly, however, the QHE could only have been
observed at liquid-helium temperatures. Here, we show that in graphene - a
single atomic layer of carbon - the QHE can reliably be measured even at room
temperature, which is not only surprising and inspirational but also promises
QHE resistance standards becoming available to a broader community, outside a
few national institutions.Comment: Published in Science online 15 February 200
A quantitative comparison of in-line coating thickness distributions obtained from a pharmaceutical tablet mixing process using discrete element method and terahertz pulsed imaging
The application of terahertz pulsed imaging (TPI) in the in-line configuration to monitor the coating thickness distribution of pharmaceutical tablets has the potential to improve the performance and quality of the spray coating process. In this study, an in-line TPI method is used to measure coating thickness distributions on pre-coated tablets during mixing in a rotating pan, and compared with results obtained numerically using the discrete element method (DEM) combined with a ray-tracing technique. The hit rates (i.e. the number of successful coating thickness measurements per minute) obtained from both terahertz in-line experiments and the DEM/ray-tracing simulations are in good agreement, and both increase with the number of baffles in the mixing pan. We demonstrate that the coating thickness variability as determined from the ray-traced data and the terahertz in-line measurements represents mainly the intra-tablet variability due to relatively uniform mean coating thickness across tablets. The mean coating thickness of the ray-traced data from the numerical simulations agrees well with the mean coating thickness as determined by the off-line TPI measurements. The mean coating thickness of in-line TPI measurements is slightly higher than that of off-line measurements. This discrepancy can be corrected based on the cap-to-band surface area ratio of the tablet and the cap-to-band sampling ratio obtained from ray-tracing simulations: the corrected mean coating thickness of the in-line TPI measurements shows a better agreement with that of off-line measurements
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