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  • Resultat 1-10 av 66
  • [1]234567Nästa
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  • Arpaia, Riccardo, 1985, et al. (författare)
  • Improved Nanopatterning for YBCO Nanowires Approaching the Depairing Current
  • 2013
  • Ingår i: IEEE Transactions on Applied Superconductivity. - 1051-8223. ; 23:3
  • Tidskriftsartikel (refereegranskat)abstract
    • An improved nanopatterning procedure has been developed to obtain YBa2Cu3O7-x nanowires with cross-sections as small as 50 x 50 nm(2), protected by an Au capping layer. To probe the effective role of the Au protecting layer, we have measured the current-voltage characteristics and the resistive transition in temperature of the nanowires. Critical current densities up to 108 A/cm(2) have been achieved at T = 4.2 K, approaching the theoretical depairing current limit. The resistance, measured as a function of temperature close to T-c, has been fitted with a thermal activated phase slip model, including the effect of the gold layer. The extracted values of the superconducting coherence length and of the London penetration depth give current densities consistent with the measured ones. These results cannot be achieved with nanowires without the Au capping layer.
  • Arzeo, Marco, 1986, et al. (författare)
  • Microwave losses in YBCO coplanar waveguide resonators at low power and millikelvin range
  • 2015
  • Ingår i: IEEE Transactions on Applied Superconductivity. - 1051-8223. ; 25:3
  • Konferensbidrag (refereegranskat)abstract
    • We have investigated the temperature dependence of microwave losses in the low-power limit and millikelvin temperature range of a thin-film YBa2Cu3O7-x (YBCO) λ/2 coplanar waveguide resonator patterned on a (La0.3Sr0.7) (Al0.65Ta0.35)O3 (LSAT) substrate covered by a CeO2 seed layer. The unloaded quality factor is mainly governed by the surface resistance of the YBCO film and the dielectric losses caused by resonant absorption due to a bath of two-level fluctuators in the dielectrics. The value of the unloaded quality factor at 20 mK and low power, i.e., Q0∼2000, allows for the realization of YBCO microwave quantum circuits implementing biepitaxial grain-boundary Josephson junctions.
  • Baghdadi, Reza, 1984, et al. (författare)
  • Toward YBa2Cu3O7-δ nanoscale structures for hybrid devices
  • 2015
  • Ingår i: IEEE Transactions on Applied Superconductivity. - 1051-8223. ; 25:3
  • Tidskriftsartikel (refereegranskat)abstract
    • An ex situ ozone annealing has been applied both on YBa2Cu3O7-d (YBCO) films and nanowires. From the investigation on bare films, by measuring the superconducting resistive transition in temperature and the X-ray diffraction pattern, we have observed that the ozonation can be a powerful tool to oxygenate the YBCO structure. To probe the effective role of this reactive annealing on nanostructures, we have fabricated nanowires with widths down to 100 nm, covered by a 20-nm-thick Au layer. We have compared the critical current density and the broadening of the resistance transition measured before and after the ozone treatment, concluding that the ozone is instrumental in recovering very high quality superconducting properties inside the nanostructures, which were degraded by the oxygen out-diffusion occurring during the nanopatterning.
  • Bevilacqua, Stella, 1981, et al. (författare)
  • MgB2 Hot-Electron Bolometer Mixers at Terahertz Frequencies
  • 2015
  • Ingår i: IEEE Transactions on Applied Superconductivity. - 1051-8223. ; 25:3, s. 2301104-
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we compare the performance of MgB2 Hot-Electron Bolometer Mixers operating at Local Oscillator frequencies of 0.6 and 1.63 THz. The minimum noise temperatures that were obtained are 700 and 1150 K for 0.6 and 1.63 THz, respectively. The receiver noise bandwidth is of the order of 2.2-3 GHz for 10-nm-thick HEB devices with a Tc of 8.5 K. Sub-micrometer size HEBs were also fabricated with no degradation of the initial film quality when a 20-nm MgB2 film with a Tc of 22 K was used. In the direct detection mode, the maximum voltage responsivity is in the range of 1-2 kV/W at 1.63 THz and the optimal bias current is around 1/4-1/3 of the Ic at 4.2 K.
  • Bevilacqua, Stella, 1981, et al. (författare)
  • Wideband MgB2 Hot-Electron Bolometer Mixers: IF Impedance Characterisation and Modeling
  • 2016
  • Ingår i: IEEE Transactions on Applied Superconductivity. - 1051-8223. ; 26:3, s. 2300105-
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper we present a method for low signal S11 parameter vector measurements of a cryogenic device in the microwave frequency range. In particular, the intermediate frequency (IF) impedance of MgB2 Hot-electron Bolometer (HEB) mixers was investigated over a frequency range of 100 MHz to 10 GHz. A new cryogenic calibration technique, which employs the HEB as a calibration kitandrequires two consecutive thermal cycles, was developed for this purpose.The real part of measured IF impedance showed a strong correlationwith the differential resistance (dV/dI) obtained from the dc I-V curves while the imaginary partwas capacitive for almost the entire frequency range.
  • Born, D., et al. (författare)
  • CaBaCuO ultrathin films and junctions
  • 2007
  • Ingår i: IEEE Transactions on Applied Superconductivity. - 1051-8223. ; 17:2/3, s. 3581-3584
  • 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).
  • Branny, Artur, et al. (författare)
  • X-Ray Induced Secondary Particle Counting With Thin NbTiN Nanowire Superconducting Detector
  • 2021
  • Ingår i: IEEE transactions on applied superconductivity (Print). - : Institute of Electrical and Electronics Engineers (IEEE). - 1051-8223 .- 1558-2515. ; 31:4
  • Tidskriftsartikel (refereegranskat)abstract
    • We characterized the performance of abiased superconducting nanowire to detect X-ray photons. The device, made of a 10 nm thin NbTiN film and fabricated on a dielectric substrate (SiO2, Nb3O5) detected 1000 times larger signal than anticipated from direct X-ray absorption. We attributed this effect to X-ray induced generation of secondary particles in the substrate. The enhancement corresponds to an increase in the flux by the factor of 3.6, relative to a state-of-the-art commercial X-ray silicon drift detector. The detector exhibited 8.25 ns temporal recovery time and 82 ps timing resolution, measured using optical photons. Our results emphasize the importance of the substrate in superconducting X-ray single photon detectors.
  • Casalbuoni, Sara, et al. (författare)
  • COLDDIAG: A Cold Vacuum Chamber for Diagnostics
  • 2011
  • Ingår i: IEEE Transactions on Applied Superconductivity. - : IEEE - Institute of Electrical and Electronics Engineers Inc.. - 1051-8223. ; 21:3, s. 2300-2303
  • Tidskriftsartikel (refereegranskat)abstract
    • One of the still open issues for the development of superconducting insertion devices is the understanding of the heat load induced by the beam passage. With the aim of measuring the beam heat load to a cold bore and in order to gain a deeper understanding in the beam heat load mechanisms, a cold vacuum chamber for diagnostics is under construction. We plan to have access with the same set-up to a number of different diagnostics, so we are implementing: i) retarding field analysers to measure the electron flux, ii) temperature sensors to measure the total heat load, iii) pressure gauges, iv) and mass spectrometers to measure the gas content. The inner vacuum chamber will be removable in order to test different geometries and materials. COLDDIAG is built to fit in a short straight section at ANKA, but we are proposing its installation in different synchrotron light sources with different energies and beam characteristics. A first installation in DIAMOND is planned in June 2011. Here we describe the technical design report of this device and the planned measurements with beam.
  • Cayado, Pablo, et al. (författare)
  • Improved Performance of CSD-Grown Y1-xGdxBa2Cu3O7-BaHfO3 Nanocomposite Films on Ni5W Substrates
  • 2020
  • Ingår i: IEEE transactions on applied superconductivity (Print). - 1051-8223 .- 1558-2515. ; 30:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Y1-xGdxBa2Cu3O7-BaHfO3 (YGBCO-BHO) nanocomposite films containing 12 mol% BHO nanoparticles and different amounts of Gd,x, were grown by Chemical Solution Deposition (CSD) on Ni5W substrates in order to investigate the impact of the rare-earth stoichiometry on the structure and superconducting properties of these films. For Gd contentsx>0.5, epitaxial YGBCO-BHO films with an approximate thickness of 270 nm self-field critical current density Jc at 77 K∼1,5 MA/cm² were obtained. The field dependence of the critical current density Jc (B) shows a much larger accommodation field and lower exponents α in Jc∼B−α values compared to pristine YBCO films. This is both due to the high amount of individual nanoparticles in the matrix as observed in TEM images and thehigher critical temperatures Tc. The results show that the CSD is a potential candidate for the preparation of REBCO films in long-length coated conductors.
  • Chukharkin, Maxim, 1980, et al. (författare)
  • Improvement of Ultra-Low Field Magnetic Resonance Recordings With a Multilayer Flux-Transformer-Based High-T-C SQUID Magnetometer
  • 2013
  • Ingår i: Ieee Transactions on Applied Superconductivity. - 1051-8223. ; 23:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We have developed a multilayer flux-transformer-based high-T-C SQUID (flip-chip) magnetometer that improves signal-to-noise-ratios (SNR) in ultra-low field magnetic resonance (ulf-MR) recordings of protons in water. Direct ulf-MR-based benchmarking of the flip-chip versus a standard planar high-T-C SQUID magnetometer resulted in improvement of the SNR by a factor of 2. This gain is attributable to the improved transformation coefficient (1.9 vs 5.3 nT/Phi(0)) that increased the signal available to the flip-chip sensor and to the lower noise at the measurement frequency (15 vs 25 fT/Hz(1/2) at 4 kHz). The improved SNR can lead to better spectroscopic resolution, lower imaging times, and higher resolution in ulf-MR imaging systems based on high-T-C SQUID technology. The experimental details of the sensors, calibration, and ulf-MR benchmarking are presented in this report.
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