86 research outputs found
Chaos in Andreev Billiards
A new type of classical billiard - the Andreev billiard - is investigated
using the tangent map technique. Andreev billiards consist of a normal region
surrounded by a superconducting region. In contrast with previously studied
billiards, Andreev billiards are integrable in zero magnetic field, {\it
regardless of their shape}. A magnetic field renders chaotic motion in a
generically shaped billiard, which is demonstrated for the Bunimovich stadium
by examination of both Poincar\'e sections and Lyapunov exponents. The issue of
the feasibility of certain experimental realizations is addressed.Comment: ReVTeX3.0, 4 pages, 3 figures appended as postscript file (uuencoded
with uufiles
Live Broadcasting of High Definition Audiovisual Content Using HDTV over Broadband IP Networks
The current paper focuses on validating an implementation of a
state-of-the art audiovisual (AV) technologies setup for live broadcasting of cultural shows, via broadband Internet. The main objective of the work was to study, configure, and setup dedicated audio-video equipment for the processes of capturing, processing, and transmission of
extended resolution and high fidelity AV content in order to increase realism and achieve maximum audience sensation. Internet2 and GEANT broadband telecommunication networks were selected as the
most applicable technology to deliver such traffic workloads. Validation procedures were conducted in
combination with metric-based quality of service (QoS) and quality of experience (QoE) evaluation
experiments for the quantification and the perceptual interpretation of the quality achieved during
content reproduction. The implemented system was successfully applied in real-world applications,
such as the transmission of cultural events from Thessaloniki Concert Hall throughout
Greece as well as the reproduction of Philadelphia
Orchestra performances (USA) via Internet2 and GEANT backbones
Diffusive conductors as Andreev interferometers
We present a novel mechanism of phase-dependent electric transport in
diffusive normal metal-superconductor structures. We provide a detailed
theoretical and numerical analysis of recent unexplained experiments
essentially explaining them.Comment: Self extracting file, 7 pages latex and 4 postscript figures. The
paper is also available at http://www.tn.tudelft.nl/tn/thspap.html In this
revision we resolved some printing problems concerning figures 2 and
Josephson current through a Luttinger liquid
We study the Josephson effect through a one-dimensional system of interacting
electrons, connected to two superconductors by tunnel junctions. The
interactions are treated in the framework of the one-channel Luttinger model.
At zero temperature, the Josephson critical current is found to decay
algebraically with increasing distance between the junctions. The exponent is
proportional to the strength of the Coulomb interaction. If the Luttinger
liquid has a finite size, the Josephson current depends on the total number of
electrons modulo 4. These parity effects are studied for the ring, coupled
capacitively to a gate-voltage and threaded by a magnetic flux. The Josephson
current changes continuously as a function of the gate voltage and {\em
stepwise} as a function of the magnetic flux. The electron-electron interaction
introduces {\em qualitatively} new features compared to the non-interacting
case.Comment: 8 pages REVTEX , 4 figures available upon reques
Re-entrance of the metallic conductance in a mesoscopic proximity superconductor
We present an experimental study of the diffusive transport in a normal metal
near a superconducting interface, showing the re-entrance of the metallic
conductance at very low temperature. This new mesoscopic regime comes in when
the thermal coherence length of the electron pairs exceeds the sample size.
This re-entrance is suppressed by a bias voltage given by the Thouless energy
and can be strongly enhanced by an Aharonov Bohm flux. Experimental results are
well described by the linearized quasiclassical theory.Comment: improved version submitted to Phys. Rev. lett., 4 pages, 5 included
epsf figure
Interband transitions in InxGa1-xAs/In0.52Al0.48As single quantum wells studied by room-temperature modulation spectroscopy
Room-temperature phototransmittance and electrotransmittance of single quantum wells of InxGa1-xAs with In0.52Al0.48As barriers have been used to study the excitonic interband transitions between the confined conduction- and valence-band states. Peak assignment has been confirmed by photocurrent spectroscopy. The lattice-matched (x=0.53) and strained (x=0.6) structures were considered for two different well widths of 50 and 250 Ã…. Transition energies and broadening parameters were measured from the spectra of the wide well samples and studied as a function of the principal quantum number. Reasonably good agreement between theory and experiment has been achieved by using published values of the electronic band-structure parameters. An observed monotonic increase of the linewidth with the quantum number has been associated with the presence of well-width fluctuations due to rough interfaces
Phase coherent transport in hybrid superconducting structures: the case of d-wave superconductors
We examine the effect of d-wave symmetry on zero bias anomalies in
normal-superconducting tunnel junctions and phase-periodic conductances in
Andreev interferometers. In the presence of d-wave pairing, zero-bias anomalies
are suppressed compared with the s-wave case. For Andreev interferometers with
aligned islands, the phase-periodic conductance is insensistive to the nature
of the pairing, whereas for non-aligned islands, the nature of the zero-phase
extremum is reversed.Comment: 10 Pages, Revtex. 11 postscript figures available on reques
Kinetic equation approach to diffusive superconducting hybrid devices
We present calculations of the temperature-dependent electrostatic and
chemical potential distributions in disordered normal metal-superconductor
structures. We show that they differ appreciably in the presence of a
superconducting terminal and propose an experiment to measure these two
different potential distributions. We also compute the resistance change in
these structures due to a recently proposed mechanism which causes a finite
effect at zero temperature. The relative resistance change due to this effect
is of the order of the interaction parameter in the normal metal. Finally a
detailed calculation of the resistance change due to the temperature dependence
of Andreev reflection in diffusive systems is presented. We find that the
maximal magnitude due to this thermal effect is in general much larger than the
magnitude of the novel effect.Comment: 11 pages LaTeX including 8 Postscript figures. A copy of the file is
also available at http://www.tn.tudelft.nl/tn/thssci.htm
Reflectionless tunneling in ballistic normal-metal--superconductor junctions
We investigate the phenomenon of reflectionless tunneling in ballistic
normal-metal--superconductor (NS) structures, using a semiclassical formalism.
It is shown that applied magnetic field and superconducting phase difference
both impair the constructive interference leading to this effect, but in a
qualitatively different way. This is manifested both in the conductance and in
the shot noise properties of the system considered. Unlike diffusive systems,
the features of the conductance are sharp, and enable fine spatial control of
the current, as well as single channel manipulations. We discuss the
possibility of conducting experiments in ballistic semiconductor-superconductor
structures with smooth interfaces and some of the phenomena, specific to such
structures, that could be measured. A general criterion for the barrier at NS
interfaces, though large, to be effectively transparent to pair current is
obtained.Comment: published versio
Patient Contact Recall after SARS Exposure
We reinterviewed healthcare workers who had been exposed to a patient with severe acute respiratory syndrome (SARS) in an intensive care unit to evaluate the effect of time on recall reliability and willingness to report contact activities and infection control precautions. Healthcare workers reliably recalled events 6 months after exposure
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