| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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