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Träfflista för sökning "WFRF:(Lombardi Floriana 1967) ;pers:(Tagliacozzo A.)"

Sökning: WFRF:(Lombardi Floriana 1967) > Tagliacozzo A.

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1.
  • Galletti, L., et al. (författare)
  • Influence of topological edge states on the properties of Al/Bi2Se3/Al hybrid Josephson devices
  • 2014
  • Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 89:13
  • Tidskriftsartikel (refereegranskat)abstract
    • In superconductor-topological insulator-superconductor hybrid junctions, the barrier edge states are expected to be protected against backscattering, to generate unconventional proximity effects, and, possibly, to signal the presence of Majorana fermions. The standards of proximity modes for these types of structures have to be settled for a neat identification of possible new entities. Through a systematic and complete set of measurements of the Josephson properties we find evidence of ballistic transport in coplanar Al-Bi2Se3-Al junctions that we attribute to a coherent transport through the topological edge state. The shunting effect of the bulk only influences the normal transport. This behavior, which can be considered to some extent universal, is fairly independent of the specific features of superconducting electrodes. A comparative study of Shubnikov-de Haas oscillations and scanning tunneling spectroscopy gave an experimental signature compatible with a two-dimensional electron transport channel with a Dirac dispersion relation. A reduction of the size of the Bi2Se3 flakes to the nanoscale is an unavoidable step to drive Josephson junctions in the proper regime to detect possible distinctive features of Majorana fermions.
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2.
  • Galletti, L., et al. (författare)
  • Josephson effect in Al/Bi2Se3/Al coplanar hybrid devices
  • 2014
  • Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 503, s. 162-165
  • Tidskriftsartikel (refereegranskat)abstract
    • The edge states of Topological Insulators (TI) are protected against backscattering, thanks to the topological properties arising from their band structure. Coupling a TI to a superconductor (S) can induce unconventional effects, including the creation of Majorana bound states (MBS). The fabrication of coplanar hybrid devices is a fundamental step to pave the way to the understanding of proximity effects in topologically non-trivial systems, and to a large variety of experiments aimed at the possible detection of MBS. We discuss the feasibility and some relevant properties of Al-Bi2Se3-Al coplanar proximity devices. Special attention is devoted to the design of the junction, aimed at enhancing the coupling between the electrodes and the TI.
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3.
  • Jouault, B., et al. (författare)
  • Josephson Coupling in Junctions Made of Monolayer Graphene Grown on SiC
  • 2016
  • Ingår i: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1947 .- 1557-1939. ; 29:5, s. 1145-1150
  • Tidskriftsartikel (refereegranskat)abstract
    • Chemical vapor deposition has proved to be successful in producing graphene samples on silicon carbide (SiC) homogeneous at the centimeter scale in terms of Hall conductance quantization. Here, we report on the realization of co-planar diffusive Al/ monolayer graphene/ Al junctions on the same graphene sheet, with separations between the electrodes down to 200 nm. Robust Josephson coupling has been measured for separations not larger than 300 nm. Transport properties are reproducible on different junctions and indicate that graphene on SiC substrates is a concrete candidate to provide scalability of hybrid Josephson graphene/superconductor devices.
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4.
  • Massarotti, D., et al. (författare)
  • Breakdown of the escape dynamics in Josephson junctions
  • 2015
  • Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 92:5
  • Tidskriftsartikel (refereegranskat)abstract
    • We have identified anomalous behavior of the escape rate out of the zero-voltage state in Josephson junctions with a high critical current density J(c). For this study we have employed YBa2Cu3O7-x grain boundary junctions, which span a wide range of J(c) and have appropriate electrodynamical parameters. Such high Jc junctions, when hysteretic, do not switch from the superconducting to the normal state following the expected stochastic Josephson distribution, despite having standard Josephson properties such as a Fraunhofer magnetic field pattern. The switching current distributions (SCDs) are consistent with nonequilibrium dynamics taking place on a local rather than a global scale. This means that macroscopic quantum phenomena seem to be practically unattainable for high Jc junctions. We argue that SCDs are an accurate means to measure nonequilibrium effects. This transition from global to local dynamics is of relevance for all kinds of weak links, including the emergent family of nanohybrid Josephson junctions. Therefore caution should be applied in the use of such junctions in, for instance, the search for Majorana fermions.
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5.
  • Massarotti, D., et al. (författare)
  • Hysteretic Critical State in Coplanar Josephson Junction with Monolayer Graphene Barrier
  • 2017
  • Ingår i: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1947 .- 1557-1939. ; 30:1, s. 5-14
  • Tidskriftsartikel (refereegranskat)abstract
    • Coplanar Al/graphene/Al junctions fabricated on the same graphene sheet deposited on silicon carbide (SiC), show robust Josephson coupling at subKelvin temperature, when the separations between the electrodes is below 400 nm. Remarkably, a hysteretic Critical State sets in when ramping an orthogonal magnetic field, with a sudden collapse of the Josephson critical current I (c) when turning the field on, and a revival of I (c) when inverting the sweep. Similar hysteresis can be found in granular superconducting films which may undergo the Berezinskii-Kosterlitz-Thouless transition. Here, we give quantitative arguments to prove that this odd behavior of the magnetoconductance gives evidence for an incipient Berezinskii-Kosterlitz-Thouless transition with drift and pinning of fluctuating free vortices induced by the current bias.
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6.
  • Massarotti, D., et al. (författare)
  • Incipient Berezinskii-Kosterlitz-Thouless transition in two-dimensional coplanar Josephson junctions
  • 2016
  • Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 94:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Superconducting hybrid junctions are revealing a variety of effects. Some of them are due to the special layout of these devices, which often use a coplanar configuration with relatively large barrier channels and the possibility of hosting Pearl vortices. A Josephson junction with a quasi-ideal two-dimensional barrier has been realized by growing graphene on SiC with Al electrodes. Chemical vapor deposition offers centimeter size monolayer areas where it is possible to realize a comparative analysis of different devices with nominally the same barrier. In samples with a graphene gap below 400 nm, we have found evidence of Josephson coherence in the presence of an incipient Berezinskii-Kosterlitz-Thouless transition. When the magnetic field is cycled, a remarkable hysteretic collapse and revival of the Josephson supercurrent occurs. Similar hysteresis are found in granular systems and are usually justified within the Bean critical state model (CSM). We show that the CSM, with appropriate account for the low-dimensional geometry, can partly explain the odd features measured in these junctions.
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7.
  • Massarotti, D., et al. (författare)
  • What happens in Josephson junctions at high critical current densities
  • 2017
  • Ingår i: Fizika Nizkih Temperatur. - : AIP Publishing. - 1816-0328 .- 0132-6414. ; 43:7, s. 816-823
  • Tidskriftsartikel (refereegranskat)abstract
    • The impressive advances in material science and nanotechnology are more and more promoting the use of exotic barriers and/or superconductors, thus paving the way to new families of Josephson junctions. Semiconducting, ferromagnetic, topological insulator and graphene barriers are leading to unconventional and anomalous aspects of the Josephson coupling, which might be useful to respond to some issues on key problems of solid state physics. However, the complexity of the layout and of the competing physical processes occurring in the junctions is posing novel questions on the interpretation of their phenomenology. We classify some significant behaviors of hybrid and unconventional junctions in terms of their first imprinting, i.e. current-voltage curves, and propose a phenomenological approach to describe some features of junctions characterized by relatively high critical current densities Jc. Accurate arguments on the distribution of switching currents will provide quantitative criteria to understand physical processes occurring in high-Jc junctions. These notions are universal and apply to all kinds of junctions. PACS: 74.72.-h Cuprate superconductors; 85.25.Cp Josephson devices; 74.50.+r Tunneling phenomena; Josephson effects.
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8.
  • Stornaiuolo, D., et al. (författare)
  • Advances in YBa2Cu3O7-delta grain boundary biepitaxial Josephson junctions: Transport properties and mesoscopic effects
  • 2007
  • Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 17:2, s. 225-228
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the latest developments in the study of transport properties of YBa2CU3O7-delta (YBCO)-based grain boundary (GB) biepitaxial Josephson junctions. We have successfully extended the fabrication process s,. originally developed for (110) oriented SrTiO3 substrates, to (110) oriented LaAlO3 substrates in view of microwave applications. We will report, also, on the observation of conductance fluctuations, we believe related to the coherent diffusion of quasi-particles across the GB. These results, together with the recent observation of macroscopic quantum tunneling and energy level quantization in these Junctions, could help cast some light on the mechanism involved in transport across grain boundaries and in revising the role and the effect of quasi particles in d-wave transport.
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9.
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10.
  • Tafuri, F., et al. (författare)
  • Coherent quasiparticle transport in grain boundary junctions employing high-T-c superconductors
  • 2006
  • Ingår i: Microelectronics. - : Elsevier BV. - 0026-2692. ; 39:8, s. 1066-1069
  • Konferensbidrag (refereegranskat)abstract
    • Magneto-fluctuations of the normal resistance R-N have been reproducibly observed in YBa2Cu3O7-delta biepitaxial grain boundary junctions at low temperatures. We attribute them to mesoscopic transport in narrow channels across the grain boundary line, occurring even in the presence of large voltage drops. The Thouless energy appears to be the relevant energy scale. Possible implications on the understanding of coherent transport of quasiparticles in high critical temperature superconductors (HTS) and of the dissipation mechanisms are discussed. (c) 2007 Elsevier Ltd. All rights reserved.
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