| 1. |
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| 2. |
- Massarotti, D., et al.
(författare)
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What happens in Josephson junctions at high critical current densities
- 2017
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Ingår i: Fizika Nizkih Temperatur. - : AIP Publishing. - 1816-0328 .- 0132-6414. ; 43:7, s. 816-823
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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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| 3. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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High-temperature superconducting nanowires for photon detection
- 2015
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 509, s. 16-21
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Tidskriftsartikel (refereegranskat)abstract
- The possible use of high-temperature superconductors (HTS) for realizing superconducting nanowire single-photon detectors is a challenging, but also promising, aim because of their ultrafast electron relaxation times and high operating temperatures. The state-of-the-art HTS nanowires with a 50-nm thickness and widths down to 130 nm have been fabricated and tested under a 1550-nm wavelength laser irradiation. Experimental results presenting both the amplitude and rise times of the photoresponse signals as a function of the normalized detector bias current, measured in a wide temperature range, are discussed. The presence of two distinct regimes in the photoresponse temperature dependence is clearly evidenced, indicating that there are two different response mechanisms responsible for the HTS photoresponse mechanisms.
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| 4. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Highly homogeneous YBCO/LSMO nanowires for photoresponse experiments
- 2014
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 27:4
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Tidskriftsartikel (refereegranskat)abstract
- By using nanolithography and a soft etching procedure, we have realized YBa2Cu3O7-x/La0.7Sr0.3MnO3 (YBCO/LSMO) nanowires, with cross sections down to 100 x 50 nm(2) that ensure the cover age of areas up to 10 x 30 mu m(2). The LSMO layer acts as a capping for YBCO, minimizing the degradation of the superconducting properties taking place during the patterning; moreover, as a ferromagnetic manganite, it is expected to accelerate the relaxation dynamics of quasiparticles in YBCO, making such a system potentially attractive for applications in superconducting ultrafast optoelectronics. The reproducibility of the values of the critical current densities measured in different devices with the same geometry makes our nanowires ideal candidates for photoresponse experiments. First measurements have shown a satisfactory photoresponse from YBCO/LSMO devices.
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| 5. |
- Barone, A., et al.
(författare)
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Macroscopic quantum phenomena in Josephson structures
- 2010
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 36:10-11, s. 876-883
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Tidskriftsartikel (refereegranskat)abstract
- The Josephson effect is a probe with unparalleled capabilities for the study of a variety of macroscopic quantum phenomena. This is a survey of important achievements and challenging trends, in particular macroscopic quantum tunneling and energy level quantization. We focus on high-T-C superconducting structures and recent research on nanostructures.
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| 6. |
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| 7. |
- Born, D., et al.
(författare)
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CaBaCuO ultrathin films and junctions
- 2007
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 17:2/3, s. 3581-3584
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Tidskriftsartikel (refereegranskat)abstract
- We investigated transport properties of ultrathin CaBaCuO (CBCO) bridges, focusing on vortex dynamics, and Josephson bicrystal junctions. The CBCO films used are composed of a stacking sequence of two structural subunits having different functions, namely a Ba-based charge reservoir (CR) block and a Ca-based infinite layer (IL) superconducting block. SQUID microscopy investigations of these films provide Pearl lengths A more than the bridge widths. Measuring current-voltage characteristics we found evidence that at high temperatures the vortices are thermally activated at the edge of the bridge and pushed in, causing dissipation and a power-law dependence of the voltage from the current. At lower temperatures, the experimental curves change their shape. We compared these data with the predicted behavior for vortex quantum tunneling and we found very good agreement. Moreover, we have realized Josephson junctions composed of only a few superconducting CuO2 planes. The CBCO films used in these experiments are only 8 nm thick and have six superconducting CUO2 planes. The simple structure of the GB allows a reliable estimation of the coupling along the ab planes of the CuO2. We calculate for 24 degrees symmetric and asymmetric cases a critical current density per plane of about (1-3) kA/cm(2).
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| 8. |
- Cedergren, Karin, 1975, et al.
(författare)
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Interplay between Static and Dynamic Properties of Semifluxons in YBa2Cu3O7−δ 0−π Josephson Junctions
- 2010
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 104:17, s. 177003 -
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the static and dynamic properties of long YBa2Cu3O7-delta 0-pi Josephson junctions and compared them with those of conventional 0 junctions. Scanning SQUID microscope imaging has revealed the presence of a semifluxon at the phase discontinuity point in 0-pi Josephson junctions. Zero field steps have been detected in the current-voltage characteristics of all junctions. Comparison with simulation allows us to attribute these steps to fluxons traveling in the junction for conventional 0 junctions and to fluxon-semifluxon interactions in the case of 0-pi Josephson junctions.
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| 9. |
- Ejrnaes, M., et al.
(författare)
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Observation of dark pulses in 10nm thick YBCO nanostrips presenting hysteretic current voltage characteristics
- 2017
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 30:12
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated several 10 nm thick and 65 nm wide YBa2Cu3O7-? (YBCO) nanostrips. The nanostrips with the highest critical current densities are characterized by hysteretic current voltage characteristics (IVCs) with a direct bistable switch from the zero-voltage to the finite voltage state. The presence of hysteretic IVCs allowed the observation of dark pulses due to fluctuations phenomena. The key role of the bistable behavior is its ability to transform a small disturbance (e.g. an intrinsic fluctuation) into a measurable transient signal, i.e. a dark pulse. On the contrary, in devices characterized by lower critical current density values, the IVCs are nonhysteretic and dark pulses have not been observed. To investigate the physical origin of the dark pulses, we have measured the bias current dependence of the dark pulse rate: The observed exponential increase with the bias current is compatible with mechanisms based on thermal activation of magnetic vortices in the nanostrip. We believe that the successful amplification of small fluctuation events into measurable signals in nanostrips of ultrathin YBCO is a milestone for further investigation of YBCO nanostrips for superconducting nanostrip single photon detectors and other quantum detectors for operation at higher temperatures.
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| 10. |
- Fittipaldi, R., et al.
(författare)
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Superconductivity in Sr2RuO4-Sr3Ru2O7 eutectic crystals
- 2008
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 83:2, s. Art. no. 27007-
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Tidskriftsartikel (refereegranskat)abstract
- Superconducting behavior has been observed in the Sr2RuO4-Sr3Ru2O7 eutectic system as grown by the flux-feeding floating-zone technique. A supercurrent flows across a single interface between Sr2RuO4 and Sr3Ru2O7 areas at distances that are far beyond those expected in a conventional proximity effect. The current-voltage characteristics within the Sr3Ru2O7 macrodomain, as extracted from the eutectic, exhibit signatures of superconductivity in the bilayered Sr3Ru2O7 region. Detailed microstructural, morphological and compositional analyses address issues on the concentration and the size of Sr2RuO4 inclusions within the Sr3Ru2O7 matrix. We speculate on the possibility of inhomogeneous superconductivity in the eutectic Sr3Ru2O7 and exotic pairing induced by the Sr2RuO4 inclusions. Copyright (C) EPLA, 2008.
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| 11. |
- Galletti, L., et al.
(författare)
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Influence of topological edge states on the properties of Al/Bi2Se3/Al hybrid Josephson devices
- 2014
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 89:13
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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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| 12. |
- Galletti, L., et al.
(författare)
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Josephson effect in Al/Bi2Se3/Al coplanar hybrid devices
- 2014
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 503, s. 162-165
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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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| 13. |
- Jouault, B., et al.
(författare)
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Josephson Coupling in Junctions Made of Monolayer Graphene Grown on SiC
- 2016
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Ingår i: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1947 .- 1557-1939. ; 29:5, s. 1145-1150
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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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| 14. |
- Longobardi, L., et al.
(författare)
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Direct Transition from Quantum Escape to a Phase Diffusion Regime in YBaCuO Biepitaxial Josephson Junctions
- 2012
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 109:5
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Tidskriftsartikel (refereegranskat)abstract
- Dissipation encodes the interaction of a quantum system with the environment and regulates the activation regimes of a Brownian particle. We have engineered grain boundary biepitaxial YBaCuO junctions to drive a direct transition from a quantum activated running state to a phase diffusion regime. The crossover to the quantum regime is tuned by the magnetic field and dissipation is described by a fully consistent set of junction parameters. To unravel phase dynamics in moderately damped systems is of general interest for advances in the comprehension of retrapping phenomena and in view of quantum hybrid technology.
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| 15. |
- Massarotti, D., et al.
(författare)
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Breakdown of the escape dynamics in Josephson junctions
- 2015
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 92:5
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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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| 16. |
- Massarotti, D., et al.
(författare)
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Hysteretic Critical State in Coplanar Josephson Junction with Monolayer Graphene Barrier
- 2017
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Ingår i: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1947 .- 1557-1939. ; 30:1, s. 5-14
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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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| 17. |
- Massarotti, D., et al.
(författare)
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Incipient Berezinskii-Kosterlitz-Thouless transition in two-dimensional coplanar Josephson junctions
- 2016
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 94:5
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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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| 18. |
- Parlato, L., et al.
(författare)
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Investigation of dark counts in innovative materials for superconducting nanowire single-photon detector applications
- 2017
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510609594 ; 10229, s. Article no 102290I-
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Konferensbidrag (refereegranskat)abstract
- The phenomenon of dark counts in nanostripes of different superconductor systems such as high-temperature superconducting YBa 2 Cu 3 O 7-x and superconductor/ferromagnet hybrids consisting of either NbN/NiCu or YBa 2 Cu 3 O 7-x /L 0.7 Sr 0.3 MnO 3 bilayers have been investigated. For NbN/NiCu the rate of dark-count transients have been reduced with respect to pure NbN nanostripes and the events were dominated by a single vortex entry from the edge of the stripe. In the case of nanostripes based on YBa 2 Cu 3 O 7-x , we have found that thermal activation of vortices was also, apparently, responsible for triggering dark-count signals.
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| 19. |
- Pepe, G. P., et al.
(författare)
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Y-Ba-Cu-O Nanostripes for Optical Photon Detection
- 2015
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628416251 ; 9504
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Konferensbidrag (refereegranskat)abstract
- Nanowires of Y-Ba-Cu-O, with the thickness of 50 nm and the width ranging from 90 nm to 500 nm have been successfully grown on lanthanum aluminate substrates for photon detection experiments. The nanowires were up to 10-mu m long and formed a meander structure, covering the area of up to 30x10 mu m(2) with a fill factor of 50%. The samples were excited using optical laser pulses at a 1550 nm wavelength and resulting photoresponse signals were measured as a function of both temperature and normalized bias current. Presence of two, distinct regimes in the photoresponse temperature dependence has been clearly evidenced, suggesting different physical mechanisms of the signal formation. Presented experimental results shed new light on prospects of implementation of high-temperature superconducting oxides in photon detection and counting.
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| 20. |
- Rotoli, G., et al.
(författare)
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Resonant phase dynamics in 0-π Sine–Gordon facets
- 2015
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer Science and Business Media LLC. - 0935-1175 .- 1432-0959. ; 27:4-5, s. 639-658
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Tidskriftsartikel (refereegranskat)abstract
- A locally phase-shifted Sine–Gordon model well accounts for the phenomenology of unconventional Josephson junctions. The phase dynamics shows resonant modes similar to Fiske modes that appear both in the presence and in the absence of the external magnetic field in standard junctions. In the latter case, they are also in competition with zero field propagation of Sine–Gordon solitons, i.e., fluxons, which give rise to the so-called zero field steps in the current–voltage (I–V) of the junction. We numerically study the I–V characteristics and the resonances magnetic field patterns for some different faceting configurations, in various dissipative regimes, as a function of temperature. The simulated dynamics of the phase is analyzed for lower-order resonances. We give evidence of a nontrivial dynamics due to the interaction of propagating fluxons with localized semifluxons. Numerical results are compared with experimental outcomes obtained on high-quality high-Tc grain boundary YBCO junctions.
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| 21. |
- Stornaiuolo, D., et al.
(författare)
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Advances in YBa2Cu3O7-delta grain boundary biepitaxial Josephson junctions: Transport properties and mesoscopic effects
- 2007
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 17:2, s. 225-228
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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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| 22. |
- Stornaiuolo, D., et al.
(författare)
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Fabrication and properties of sub-micrometric YBCO biepitaxial junctions
- 2009
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 150:5
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Konferensbidrag (refereegranskat)abstract
- We report on the fabrication procedure and the transport properties of submicron grain boundary biepitaxial YBCO Josephson junctions. These first results are very encouraging and justify further expectations on improved performances for such types of devices. A reduced and more controlled faceting along the grain boundary interface, for instance, will better preserve intrinsic d-wave effects, and favour the study of fluxons dynamics.
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| 23. |
- Stornaiuolo, D., et al.
(författare)
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Submicron YBaCuO biepitaxial Josephson junctions: d-wave effects and phase dynamics
- 2010
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 107:11
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Tidskriftsartikel (refereegranskat)abstract
- We report a systematic study of the transport properties of high critical temperature superconductor (HTS) biepitaxial Josephson junctions in the submicron range. Junction performances point to more uniform and reproducible devices and to better control of d-wave intrinsic properties. Outcomes promote novel insights into the transport mechanisms across grain boundaries and encourage further developments in the control of dissipation in HTS devices. The application of nanotechnology to HTS could be an additional tool to properly engineer the junction properties to match specific circuit design also in view of the integration into hybrid quantum circuits. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3388035]
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| 24. |
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| 25. |
- Tafuri, F., et al.
(författare)
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Coherent quasiparticle transport in grain boundary junctions employing high-T-c superconductors
- 2006
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Ingår i: Microelectronics. - : Elsevier BV. - 0026-2692. ; 39:8, s. 1066-1069
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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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| 26. |
- Tafuri, F., et al.
(författare)
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Mesoscopic conductance fluctuations in high-T-c grain boundary Josephson junctions: Coherent quasiparticle transport
- 2007
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 460-462:Part 1, s. 343-346
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Tidskriftsartikel (refereegranskat)abstract
- Magneto-fluctuations of the normal resistance RN have been reproducibly observed in YBa2Cu3O7-delta (HTS) biepitaxial grain boundary junctions at low temperatures. We attribute them to mesoscopic transport in narrow channels across the grain boundary line. The Thouless energy appears to be the relevant energy scale. Possible implications on the understanding of coherent transport of quasiparticles in HTS and of the dissipation mechanisms are discussed. (c) 2007 Elsevier B.V. All rights reserved.
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| 27. |
- Tafuri, F., et al.
(författare)
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Recent Achievements on the Physics of High-T cSuperconductor Josephson Junctions: Background, Perspectives and Inspiration
- 2013
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Ingår i: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1947 .- 1557-1939. ; 26:1, s. 21-41
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Forskningsöversikt (refereegranskat)abstract
- Coherent passage of Cooper pairs in a Josephson junction (JJ) above the liquid nitrogen temperature has been the first impressive revolutionary effect induced by high critical temperature superconductors (HTS) in the domain of the study of Josephson effect (JE). But this has been only the start. A d-wave order parameter has lead to significant novel insights in the physics of the JE turning into a device the notion of a pi-junction. Spontaneous currents in a frustrated geometry, Andreev bound states, long-range proximity effect have rapidly become standard terms in the study of the JE, standing as a reference bench for conventional systems based on low critical temperature superconductors (LTS) and inspiring analogies for junctions based on novel superconductors discovered in the meantime. The extreme richness of the physics of HTS JJs has not been adequately supported by the expected impact in the applications, the main reason lying in the complexity of these materials and in the consequent unsatisfactory yield and reproducibility of the performances of the JJs within the required limits. The continuous progress in material science, and specifically in the realization of oxide multi-layers, and in nanotechnologies applied to superconductors, accompanied by the advances in a better understanding of the properties of HTS and of HTS devices, has as a matter of fact opened possible novel scenarios and interest in the field. We intend to give a brief overview on interesting new problems concerning HTS JJs of inspiration also for other systems. We also review some ideas and experimental techniques on macroscopic quantum decay phenomena occurring in Josephson structures. The attention is mainly addressed to intermediate levels of dissipation, which characterize a large majority of low critical current Josephson devices and are therefore an unavoidable consequence of nanotechnology applied more and more to Josephson devices.
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| 28. |
- Tagliacozzo, A., et al.
(författare)
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Mesoscopic conductance fluctuations in YBa2Cu3O7-delta grain boundary junctions at low temperature
- 2009
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 79:2
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Tidskriftsartikel (refereegranskat)abstract
- The magnetoconductance in YBa2Cu3O7-delta grain boundary Josephson junctions displays fluctuations at low temperatures of mesoscopic origin. The morphology of the junction suggests that transport occurs in narrow channels across the grain boundary line with a large Thouless energy. Nevertheless the measured fluctuation amplitude decreases quite slowly when increasing the voltage up to values about 20 times the Thouless energy, of the order of the nominal superconducting gap. Our findings show the coexistence of supercurrent and quasiparticle current in the junction conduction even at high nonequilibrium conditions. Model calculations confirm the reduced role of quasiparticle relaxation at temperatures up to 3 K.
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| 29. |
- Tagliacozzo, A., et al.
(författare)
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Observation of mesoscopic conductance fluctuations in YBa2Cu3O7-delta grain boundary Josephson junctions
- 2007
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 75:1, s. 012507-
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Tidskriftsartikel (refereegranskat)abstract
- Magnetofluctuations of the normal-state resistance R-N have been reproducibly observed in high-critical-temperature superconductor (HTS) grain boundary junctions at low temperatures. We attribute them to mesoscopic transport in narrow channels across the grain boundary line. The Thouless energy appears to be the relevant energy scale. Our findings have significant implications for quasiparticle relaxation and coherent transport in HTS grain boundaries.
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