Fluctuation Effects in High Sheet Resistance Superconducting Films

As the normal state sheet resistance, $R_n$, of a thin film superconductor increases, its superconducting properties degrade. For $R_n\simeq h/4e^2$ superconductivity disappears and a transition to a nonsuperconducting state occurs. We present electron tunneling and transport measurements on ultrathin, homogeneously disordered superconducting films in the vicinity of this transition. The data provide strong evidence that fluctuations in the amplitude of the superconducting order parameter dominate the tunneling density of states and the resistive transitions in this regime. We briefly discuss possible sources of these amplitude fluctuation effects. We also describe how the data suggest a novel picture of the superconductor to nonsuperconductor transition in homogeneous 2D systems.Comment: 11 pages, 5 figure

Observation of a subgap density of states in superconductor-normal metal bilayers in the Cooper limit

We present transport and tunneling measurements of Pb-Ag bilayers with thicknesses, $d_{Pb}$ and $d_{Ag}$, that are much less than the superconducting coherence length. The transition temperature, $T_c$, and energy gap, $\Delta$, in the tunneling Density of States (DOS) decrease exponentially with $d_{Ag}$ at fixed $d_{Pb}$. Simultaneously, a DOS that increases linearly from the Fermi energy grows and fills nearly 40% of the gap as $T_c$ is 1/10 of $T_c$ of bulk Pb. This behavior suggests that a growing fraction of quasiparticles decouple from the superconductor as $T_c$ goes to 0. The linear dependence is consistent with the quasiparticles becoming trapped on integrable trajectories in the metal layer.Comment: 5 pages and 4 figures. This version is just the same as the old version except that we try to cut the unnecessary white space in the figures and make the whole paper look more compac

The interference effect of concurrent working memory task on visual inhibitory control

We examined the interference between inhibitory control of a saccadic eye movement and a working memory task. This study was motivated by the observation that people are suscep-tible to cognitive errors when they are preoccupied. Subjects were instructed to make an anti-saccade, or to look in the opposite direction of a visual stimulus, thereby exercising inhibito-ry control over the reflexive eye movement towards a salient object. At the same time, the subjects were instructed to memorize a random sequence of digits that were read out to them, thereby engaging their working memory. We measured the success of an eye movement by rapidly switching between images and asking the subjects what they saw. We found that these concurrent cognitive tasks significantly degraded anti-saccade performance.We examined the interference between inhibitory control of a saccadic eye movement and a working memory task. This study was motivated by the observation that people are susceptible to cognitive errors when they are preoccupied. Subjects were instructed to make an anti-saccade, or to look in the opposite direction of a visual stimulus, thereby exercising inhibitory control over the reflexive eye movement towards a salient object. At the same time, the subjects were instructed to memorize a random sequence of digits that were read out to them, thereby engaging their working memory. We measured the success of an eye movement by rapidly switching between images and asking the subjects what they saw. We found that these concurrent cognitive tasks significantly degraded anti-saccade performance

A Theory of Object Recognition: Computations and Circuits in the Feedforward Path of the Ventral Stream in Primate Visual Cortex

We describe a quantitative theory to account for the computations performed by the feedforward path of the ventral stream of visual cortex and the local circuits implementing them. We show that a model instantiating the theory is capable of performing recognition on datasets of complex images at the level of human observers in rapid categorization tasks. We also show that the theory is consistent with (and in some case has predicted) several properties of neurons in V1, V4, IT and PFC. The theory seems sufficiently comprehensive, detailed and satisfactory to represent an interesting challenge for physiologists and modelers: either disprove its basic features or propose alternative theories of equivalent scope. The theory suggests a number of open questions for visual physiology and psychophysics

Proximity effect in granular superconductor-normal metal structures

We fabricated three-dimensional disordered Pb-Cu granular structures, with various metal compositions. The typical grain size of both metals is smaller than the superconductor and normal metal coherence lengths, thus satisfying the Cooper limit. The critical temperature of the samples was measured and compared with the critical temperature of bilayers. We show how the proximity effect theories, developed for bilayers, can be modified for random mixtures and we demonstrate that our experimental data fit well the de Gennes weak coupling limit theory in the Cooper limit. Our results indicate that, in granular structures, the Cooper limit can be satisfied over a wide range of concentrations.Comment: 15 pages, 4 figure

A New Hybrid Debugging Architecture for Eclipse

The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-14125-1_11[EN] During many years, print debugging has been the most used method for debugging. Nowadays, however, industrial languages come with a trace debugger that allows programmers to trace computations step by step using breakpoints and state viewers. Almost all modern programming environments include a trace debugger that allows us to inspect the state of a computation in any given point. Nevertheless, this debugging method has been criticized for being completely manual and time-consuming. Other debugging techniques have appeared to solve some of the problems of Trace Debugging, but they suffer from other problems such as scalability. In this work we present a new hybrid debugging technique. It is based on a combination of Trace Debugging, Algorithmic Debugging and Omniscient Debugging to produce a synergy that exploits the best properties and strong points of each technique. We describe the architecture of our hybrid debugger and our implementation that has been integrated into Eclipse as a plugin.This work has been partially supported by the Spanish Ministerio de Economía y Competitividad (Secretaria de Estado de Investigación, Desarrollo e Innovación) under grant TIN2008-06622-003-02 and by the Generalitat Valenciana under grant PROMETEO/2011/052. David Insa was partially supported by the Spanish Ministerio de Educación under FPU grant AP2010-4415.González, J.; Insa Cabrera, D.; Silva Galiana, JF. (2013). A New Hybrid Debugging Architecture for Eclipse. En Logic-Based Program Synthesis and Transformation. Springer. 183-201. doi:10.1007/978-3-319-14125-1_11S183201Swi-prolog (1987). http://www.swi-prolog.org/Netbeans (1999). http://www.netbeans.org/Eclipse (2003). http://www.eclipse.org/Omnicore codeguide (2007). http://www.omnicore.com/en/codeguide.htmBorland JBuilder (2008). http://www.embarcadero.com/products/jbuilder/Sicstus prolog spider ide (2009). https://sicstus.sics.se/spider/Caballero, R.: A Declarative Debugger of Incorrect Answers for Constraint Functional-Logic Programs. In: Proceedings of the 2005 ACM-SIGPLAN Workshop on Curry and Functional Logic Programming (WCFLP 2005), pp. 8–13. ACM Press, New York (2005)Davie, T., Chitil, O.: Hat-delta: One Right Does Make a Wrong. In: Proceedings of the 7th Symposium on Trends in Functional Programming (TFP 2006) (April 2006)Gestwicki, P., Jayaraman, B.: JIVE: Java Interactive Visualization Environment. In: Companion to the 19th Annual ACM-SIGPLAN Conference on Object-Oriented Programming Systems, Languages, and Applications (OOPSLA 2004), pp. 226–228. ACM Press, New York (2004)Giammona, D.: ORACLE ADF - Putting It Together. Technical report, ADF Declarative Debugger Archives (November 2009)Girgis, H., Jayaraman, B.: JavaDD: a Declarative Debugger for Java. Technical report,University at Buffalo (2006)González, F., De Miguel, R., Serrano, S.: Depurador Declarativo de Programas Java. Technical report, Universidad Complutense de Madrid (2006). http://eprints.ucm.es/9114/Hermanns, C., Kuchen, H.: Hybrid Debugging of Java Programs. In: Escalona, M.J., Cordeiro, J., Shishkov, B. (eds.) ICSOFT 2011. CCIS, vol. 303, pp. 91–107. Springer, Heidelberg (2013)Montebello, M., Abela, C.: Design and Implementation of a Backward-In-Time. In: Chaudhri, A.B., Jeckle, M., Rahm, E., Unland, R. (eds.) NODe-WS 2002. LNCS, vol. 2593, pp. 46–58. 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LNCS, vol. 5142, pp. 592–615. Springer, Heidelberg (2008)S. Microsystems. Java Platform Debugger Architecture - JPDA (2010). http://java.sun.com/javase/technologies/core/toolsapis/jpda/Mirghasemi, S., Barton, J., Petitpierre, C.: Debugging by lastChange. Technical report (2011). http://people.epfl.ch/salman.mirghasemiNilsson, H.: Declarative Debugging for Lazy Functional Languages. PhD thesis, Linköping, Sweden (May 1998)Nilsson, H., Fritzson, P.: Algorithmic Debugging for Lazy Functional Languages. Journal of Functional Programming 4(3), 337–370 (1994)Pothier, G.: Towards Practical Omniscient Debugging. PhD thesis, University of Chile (June 2011)Shapiro, E.: Algorithmic Program Debugging. MIT Press (1982)Silva, J.: A Survey on Algorithmic Debugging Strategies. Advances in Engineering Software 42(11), 976–991 (2011

Coherent, mechanical control of a single electronic spin

The ability to control and manipulate spins via electrical, magnetic and optical means has generated numerous applications in metrology and quantum information science in recent years. A promising alternative method for spin manipulation is the use of mechanical motion, where the oscillation of a mechanical resonator can be magnetically coupled to a spins magnetic dipole, which could enable scalable quantum information architectures9 and sensitive nanoscale magnetometry. To date, however, only population control of spins has been realized via classical motion of a mechanical resonator. Here, we demonstrate coherent mechanical control of an individual spin under ambient conditions using the driven motion of a mechanical resonator that is magnetically coupled to the electronic spin of a single nitrogen-vacancy (NV) color center in diamond. Coherent control of this hybrid mechanical/spin system is achieved by synchronizing pulsed spin-addressing protocols (involving optical and radiofrequency fields) to the motion of the driven oscillator, which allows coherent mechanical manipulation of both the population and phase of the spin via motion-induced Zeeman shifts of the NV spins energy. We demonstrate applications of this coherent mechanical spin-control technique to sensitive nanoscale scanning magnetometry.Comment: 6 pages, 4 figure

Early stage morphology of quench condensed Ag, Pb and Pb/Ag hybrid films

Scanning Tunneling Microscopy (STM) has been used to study the morphology of Ag, Pb and Pb/Ag bilayer films fabricated by quench condensation of the elements onto cold (T=77K), inert and atomically flat Highly Oriented Pyrolytic Graphite (HOPG) substrates. All films are thinner than 10 nm and show a granular structure that is consistent with earlier studies of QC films. The average lateral diameter, $\bar {2r}$, of the Ag grains, however, depends on whether the Ag is deposited directly on HOPG ($\bar {2r}$ = 13 nm) or on a Pb film consisting of a single layer of Pb grains ($\bar {2r}$ = 26.8 nm). In addition, the critical thickness for electrical conduction ($d_{G}$) of Pb/Ag films on inert glass substrates is substantially larger than for pure Ag films. These results are evidence that the structure of the underlying substrate exerts an influence on the size of the grains in QC films. We propose a qualitative explanation for this previously unencountered phenomenon.Comment: 11 pages, 3 figures and one tabl

Approaching Zero-Temperature Metallic States in Mesoscopic Superconductor-Normal-Superconductor Arrays

Systems of superconducting islands placed on normal metal films offer tunable realizations of two-dimensional (2D) superconductivity; they can thus elucidate open questions regarding the nature of 2D superconductors and competing states. In particular, island systems have been predicted to exhibit zero-temperature metallic states. Although evidence exists for such metallic states in some 2D systems, their character is not well understood: the conventional theory of metals cannot explain them, and their properties are difficult to tune. Here, we characterize the superconducting transitions in mesoscopic island-array systems as a function of island thickness and spacing. We observe two transitions in the progression to superconductivity; both transition temperatures exhibit unexpectedly strong depression for widely spaced islands. These depressions are consistent with the system approaching zero-temperature metallic states. The nature of the transitions and the state between them is explained using a phenomenological model involving the stabilization of superconductivity on each island via a weak coupling to and feedback from its neighbors.Comment: 15 pages, 5 figure