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 Å. 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