641 research outputs found
Superconductivity in heavily compensated Mg-doped InN
We report superconductivity in Mg-doped InN grown by molecular beam epitaxy. Superconductivity phase transition temperature occurs Tc = 3.97âK as determined by magnetoresistance and Hall resistance measurements. The two-dimensional (2D) carrier density of the measured sample is n2D = 9Ă1014âcmâ2 corresponding to a three-dimensional (3D) electron density of n3D = 1.8Ă1019âcmâ3 which is within the range of values between Mott transition and the superconductivity to metal transition. We propose a plausible mechanism to explain the existence of the superconductivity in terms of a uniform distribution of superconducting InN nanoparticles or nanosized indium dots forming microscopic Josephson junctions in the heavily compensated insulating bulk InN matrix
Submarine landslides on the upper southeast Australian passive continental margin â preliminary findings
The southeast Australian passive continental margin is narrow, steep and sediment-deficient, and characterized by relatively low rates of modern sedimentation. Upper slope (\u3c1200m) sediments comprise mixtures of calcareous and terrigenous sand and mud. Three of twelve sediment cores recovered from geologically-recent, submarine landslides located offshore New South Wales/Queensland (NSW/QLD) are interpreted to have sampled failure surfaces at depths of between 85 cm and 220 cm below the present-day seabed. Differences in sediment physical properties are recorded above and below the three slide-plane boundaries. Sediment taken directly above the inferred submarine landslide failure surfaces and presumed to be post-landslide, returned radiocarbon ages of 15.8 ka, 20.7 ka and 20.1 ka. The last two ages correspond to adjacent slide features, which are inferred to be consistent with their being triggered by a single event such as an earthquake. Slope stability models based on classical soil mechanics and measured sediment shearstrengths indicate that the upper slope sediments should be stable. However, multibeam sonar data reveal that many upper slope landslides occur across the margin and that submarine landsliding is a common process. We infer from these results that: a) an unidentified mechanism regularly acts to reduce the shear resistance of these sediments to the very low values required to enable slope failure, and/or b) the margin experiences seismic events that act to destabilise the slope sediments
Classical percolation fingerprints in the high-temperature regime of the integer quantum Hall effect
We have performed magnetotransport experiments in the high-temperature regime
(up to 50 K) of the integer quantum Hall effect for two-dimensional electron
gases in semiconducting heterostructures. While the magnetic field dependence
of the classical Hall law presents no anomaly at high temperatures, we find a
breakdown of the Drude-Lorentz law for the longitudinal conductance beyond a
crossover magnetic field B_c ~ 1 T, which turns out to be correlated with the
onset of the integer quantum Hall effect at low temperatures. We show that the
high magnetic field regime at B > B_c can be understood in terms of classical
percolative transport in a smooth disordered potential. From the temperature
dependence of the peak longitudinal conductance, we extract scaling exponents
which are in good agreement with the theoretically expected values. We also
prove that inelastic scattering on phonons is responsible for dissipation in a
wide temperature range going from 1 to 50 K at high magnetic fields.Comment: 14 pages + 8 Figure
Simulations of nanograting-assisted light coupling in GaN planar waveguide
The numerical simulations of nanogratings integrated with gallium nitride (GaN) planar waveguides as well as the experimental in-coupling results are presented. A simulation tool based on the eigenmode expansion method and advanced boundary conditions provided a rigorous model of 400-nm-period grating couplers. A full-vectorial Maxwell solver allowed performing a number of simulations with varying grating parameters, where coupling efficiency, reflection and transmission characteristics of device were calculated. Gratings with different etch depths and arbitrary shapes were simulated using a staircase approximation, with an optimized number of steps per single slope. For the first time, an impact of dry etch processing on GaN coupler efficiency was evaluated, due to the inclusion of the sloped sidewalls, with regard to the technological constrains. Finally, the experimental results in the visible spectrum region (lambda = 633 nm), for 400-nm-deep gratings etched in GaN waveguide, were presented together with theoretical data for binary and trapezoidal profiles of a grating, for different optical mode profiles (TE(0) divided by TE(3) modes)
Note: A miniature oscillating microbalance for sampling ice and volcanic ash from a small airborne platform
A lightweight and low power oscillating microbalance for in situ sampling of atmospheric ice and volcanic ash is described for airborne platforms. Using a freely exposed collecting wire fixed at only one end to a piezo transducer, the instrument collects airborne materials. Accumulated mass is determined from the change in natural frequency of the wire. The piezo transducer is used in a dual mode to both drive and detect the oscillation. Three independent frequency measurement techniques are implemented with an on-board microcontroller: a frequency sweep, a Fourier spectral method, and a phase-locked loop. These showed agreement to ±0.3 Hz for a 0.5 mm diameter collecting wire of 120 mm long, flown to 19 km altitude on a weather balloon. The instrument is well suited to disposable use with meteorological radiosondes, to provide high resolution vertical profiles of mass concentration
Influence of the single-particle Zeeman energy on the quantum Hall ferromagnet at high filling factors
In a recent paper [B. A. Piot et al., Phys. Rev. B 72, 245325 (2005)], we
have shown that the lifting of the electron spin degeneracy in the integer
quantum Hall effect at high filling factors should be interpreted as a
magnetic-field-induced Stoner transition. In this work, we extend the analysis
to investigate the influence of the single-particle Zeeman energy on the
quantum Hall ferromagnet at high filling factors. The single-particle Zeeman
energy is tuned through the application of an additional in-plane magnetic
field. Both the evolution of the spin polarization of the system and the
critical magnetic field for spin splitting are well described as a function of
the tilt angle of the sample in the magnetic field.Comment: Published in Phys. Rev.
Dispersive line shape in the vicinity of the {\nu} = 1 quantum Hall state: Coexistence of Knight shifted and unshifted resistively detected NMR responses
The frequency splitting between the dip and the peak of the resistively
detected nuclear magnetic resonance (RDNMR) dispersive line shape (DLS) has
been measured in the quantum Hall effect regime as a function of filling
factor, carrier density and nuclear isotope. The splitting increases as the
filling factor tends to {\nu} = 1 and is proportional to the hyperfine
coupling, similar to the usual Knight shift versus {\nu}-dependence. The peak
frequency shifts linearly with magnetic field throughout the studied filling
factor range and matches the unshifted substrate signal, detected by classical
NMR. Thus, the evolution of the splitting is entirely due to the changing
Knight shift of the dip feature. The nuclear spin relaxation time, T1, is
extremely long (hours) at precisely the peak frequency. These results are
consistent with the local formation of a {\nu} = 2 phase due to the existence
of spin singlet D complexes.Comment: to be published in Rapid Communication PR
Note on a sigma model connection with instanton dynamics
It is well known that the instanton approach to QCD generates an effective
term which looks like a three flavor determinant of quark bilinears. This has
the right behavior to explain the unusual mass and mixing of the
meson, as is often simply illustrated with the aid of a linear SU(3) sigma
model. It is less well known that the instanton analysis generates another term
which has the same transformation property but does not have a simple
interpretation in terms of this usual linear sigma model. Here we point out
that this term has an interpretation in a generalized linear sigma model
containing two chiral nonets. The second chiral nonet is taken to correspond to
mesons having two quarks and two antiquarks in their makeup. The generalized
model seems to be useful for learning about the spectrum of low lying scalar
mesons which have been emerging in the last few years. The physics of the new
term is shown to be related to the properties of an "excited" state
present in the generalized model and for which there are some experimental
candidates.Comment: reference added, minor typos correcte
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