48,543 research outputs found
Acoustic Spectroscopy of Superfluid 3He in Aerogel
We have designed an experiment to study the role of global anisotropic
quasiparticle scattering on the dirty aerogel superfluid 3He system. We observe
significant regions of two stable phases at temperatures below the superfluid
transition at a pressure of 25 bar for a 98% aerogel.Comment: 2 pages, 2 figures, accepted for publication in proceedings of Low
Temperature Conference 2
Specific Heat of Disordered He
Porous aerogel is a source of elastic scattering in superfluid 3He and
modifies the properties of the superfluid, suppressing the transition
temperature and order parameter. The specific heat jumps for the B-phase of
superfluid 3He in aerogel have been measured as a function of pressure and
interpreted using the homogeneous and inhomogeneous isotropic scattering
models. The specific heat jumps for other p-wave states are estimated for
comparison.Comment: Manuscript prepared for LT 2
Magneto-Acoustic Spectroscopy in Superfluid 3He-B
We have used the recently discovered acoustic Faraday effect in superfluid
3He to perform high resolution spectroscopy of an excited state of the
superfluid condensate. With acoustic cavity interferometry we measure the
rotation of the plane of polarization of a transverse sound wave propagating in
the direction of magnetic field from which we determine the Zeeman energy of
the excited state. We interpret the Lande g-factor, combined with the
zero-field energies of the state, using the theory of Sauls and Serene to
calculate the strength of f -wave interactions in 3He.Comment: 4 pages, 5 figures, submitted to PRL, Aug 30th, 200
Mechanism of enhanced light output in InGaN-based microlight emitting diodes
Micro-light emitting diode (LED) arrays with diameters of 4 to 20 mum have been fabricated and were found to be much more efficient light emitters compared to their broad-area counterparts, with up to five times enhancement in optical power densities. The possible mechanisms responsible for the improvement in performance were investigated. Strain relaxation in the microstructures as measured by Raman spectroscopy was not observed, arguing against theories of an increase in internal quantum efficiency due to a reduction of the piezoelectric field put forward by other groups. Optical microscope images show intense light emission at the periphery of the devices, as a result of light scattering off the etched sidewalls. This increases the extraction efficiency relative to broad area devices and boosts the forward optical output. In addition, spectra of the forward emitted light reveal the presence of resonant cavity modes [whispering gallery (WG) modes in particular] which appear to play a role in enhancing the optical output
Processing of carbon-fiber-reinforced Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass composites
Carbon-fiber-reinforced bulk metallic glass composites are produced by infiltrating liquid Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 into carbon fiber bundles with diameter of the individual fiber of 5 mum. Reactive wetting occurs by the formation of a ZrC layer around the fibers. This results in a composite with a homogeneous fiber distribution. The volume fraction of the fibers is about 50% and the density of the composite amounts to 4.0 g/cm(^3)
Anomalous Attenuation of Transverse Sound in 3He
We present the first measurements of the attenuation of transverse sound in
superfluid 3He-B. We use fixed path length interferometry combined with the
magneto-acoustic Faraday effect to vary the effective path length by a factor
of two, resulting in absolute values of the attenuation. We find that
attenuation is significantly larger than expected from the theoretical
dispersion relation, in contrast to the phase velocity of transverse sound. We
suggest that the anomalous attenuation can be explained by surface Andreev
bound states.Comment: 4 pages, 5 figures, accepted to Phys. Rev. Let
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