| 1. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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Improved Nanopatterning for YBCO Nanowires Approaching the Depairing Current
- 2013
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 23:3
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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.
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| 2. |
- Arzeo, Marco, 1986, et al.
(författare)
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Microwave losses in YBCO coplanar waveguide resonators at low power and millikelvin range
- 2015
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 25:3
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Tidskriftsartikel (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.
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| 3. |
- Baghdadi, Reza, 1984, et al.
(författare)
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Toward YBa2Cu3O7-δ nanoscale structures for hybrid devices
- 2015
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 25:3
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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.
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| 4. |
- 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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| 5. |
- galletti, luca, 1986, et al.
(författare)
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High-Transparency Al/Bi2Te3 Double-Barrier Heterostructures
- 2017
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 27:4
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated highly transparent Al/Bi2Te3/Al superconductor/normal metal/superconductor double-barrier heterostructures. Transport measurements reveal the presence of multiple Andreev reflections related to two distinct energy gaps that we identify as the induced superconducting gap in the two electrodes. The realization of high-transparency Josephson junctions with topological insulators is an important step towards the study of topological superconductivity and Majorana fermions.
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| 6. |
- Nawaz, Shahid, 1978, et al.
(författare)
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Transport Properties of YBCO Nanowires
- 2011
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 21:3, s. 164-167
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Tidskriftsartikel (refereegranskat)abstract
- We have carried out transport studies of YBa2Cu3O7-x (YBCO) nanowires. By exposing nanowires with microwaves, we see that short wires which have a flux-flow like current-voltage characteristic (IVC) clearly manifest current steps in the IVC (Shapiro steps). On the contrary, the longer wires exhibiting a resistively and capacitively shunted junction (RCSJ) model like current-voltage characteristic do not feature any Shapiro steps. The second case can be explained by taking into consideration the longer wire lengths where the wires loose coherency of flux flow due to inhomogeneity along the wire.
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| 7. |
- Rotoli, G., et al.
(författare)
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Eck-Like Resonances in High-T-c Long Faceted Josephson Junctions
- 2009
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 19:3, s. 911-915
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Tidskriftsartikel (refereegranskat)abstract
- By means of numerical simulations we study the dynamics of the phase difference in faceted long Josephson junctions. We compare our simulations with experiments on a sample of high quality high-Tc biepitaxial junctions. Adjusting junction length and dissipation to reproduce the observed data we found a significant agreement, which permits to identify the observed resonances mostly as Eck steps. Some considerations are also made on the requirements to observe flux-flow or Fiske resonances in these junctions.
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| 8. |
- 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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| 9. |
- Stornaiuolo, D, et al.
(författare)
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Sub-Micron YBa2Cu3O7-x Biepitaxial Junctions
- 2009
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 19:3, s. 174-177
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication and properties of sub-micron YBa2Cu3O7-x off-axis biepitaxial junctions. The vision behind this work is to set up a reliable nanotechnology processing to improve junctions' performances and reproducibility through the reduction of their size. We will illustrate the fabrication procedure employed and show the results obtained on samples where the transport parameters were tuned in a predictable way. Also, proofs of a clean barrier structure with few facets and low disorder were obtained.
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| 10. |
- Trabaldo, Edoardo, 1990, et al.
(författare)
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Noise Properties of YBCO Nanostructures
- 2017
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 27:4
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Tidskriftsartikel (refereegranskat)abstract
- Voltage noise measurements on close to optimally doped YBa2Cu3O7-delta nanostructures have been performed. The measured resistance noise at temperature T = 96 K (above critical temperature T-C = 85 K) shows a quadratic dependence on the bias current, e.g., the voltage power spectral density S-V alpha V-2. Moreover, the normalized voltage noise S-V/V-2 is inversely proportional to the device volume. This is a clear indication that the noise is the result of an ensemble of independent resistive fluctuators, evenly distributed within the sample volume. For our structures, we obtain a product S-V/V-2 x Vol. = const. approximate to 6 x 10-(33) m(3)/Hz resulting in a Hooge's parameter 3.4 x 10(-4), which is among the lowest reported in literature. At lower temperature, T = 2 K (well below TC) the total voltage fluctuations are given by the combined effect of critical current fluctuations and resistance fluctuations. For the critical current noise, we obtain a product S-I/IC2 x Vol. = const. approximate to 6x10(-32) m(3)/Hz. The larger value of the relative critical current noise is most probably due to the fact that the critical current is determined by edge effects whereas the resistance is given by the total volume of the device.
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