| 1. |
- 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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| 2. |
- Haugen, O., et al.
(författare)
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High resolution thermal imaging of hotspots in superconducting films
- 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. 3215-3218
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Tidskriftsartikel (refereegranskat)abstract
- Thermal imaging of hotspots in bridge structures of YbaCuO thin films is presented with micrometer resolution. Hotspots formed by passing transport currents are observed using a method based on the temperature dependence in the photoluminescence of a polymer thin film deposited on the superconductor. The hotspots are self maintained and have hysteretic behavior. An external magnetic field changes their behavior. The temperature distribution over the bridge and in its vicinity can be observed with a resolution better than 0.1 K. Also details of the experimental method will be reported.
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| 3. |
- Khosropanah, Pourya, 1971, et al.
(författare)
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Analysis of NbN Hot Electron Bolometer Receiver Noise Temperatures Above 2 THz With a Quantum Noise Model
- 2009
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 19:3, s. 274-277
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Tidskriftsartikel (refereegranskat)abstract
- This paper summarizes our receiver noise temperature data of NbN HEB mixers obtained at a number of local oscillator frequencies between 1.9 to 4.3 THz in order to verify the role of quantum noise. The experimental data show that the receiver noise temperature increases roughly linearly with frequency. At 4.3 THz, we measured a receiver noise temperature of 1300 K, which is about 6 times (hf/k B) . The noise data at different frequencies are compared to a prediction of a noise model including the contribution of quantum noise and making use of a hot-spot model for mixing. We draw a preliminary conclusion that at 4.3 THz roughly 30% of the receiver noise temperature can be ascribed to the quantum noise. However, more dedicated measurements are required in order to further support the quantum noise model for HEB mixers.
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| 4. |
- 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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| 5. |
- Shaw, M. D., et al.
(författare)
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Experimental realization of a differential charge qubit
- 2007
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 17:2, s. 109-112
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the operation of a differential single Cooper-pair box, a charge qubit consisting of two aluminum islands, isolated from ground, coupled by a pair of small-area Josephson junctions. We have tested four devices, all of which show evidence of quasiparticle poisoning. The devices are characterized with microwave spectroscopy and temperature dependence studies. © 2007 IEEE.
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| 6. |
- Snigirev, O., et al.
(författare)
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Superconducting Quantum Interference Filters as RF amplifiers
- 2007
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 17:2, s. 718-721
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Tidskriftsartikel (refereegranskat)abstract
- The superconducting Quantum Interference Filter (SQIF) is a new type of superconducting device which has been recently proposed for highly sensitive magnetometers for absolute magnetic field measurements. It benefits of very high voltage-to-field response, which is, in contrast conventional dc SQUIDs, not periodical. The SQIF can also be used as a radiofrequency amplifier in a similar way as the dc SQUID that can operate in a gigahertz frequency range. We designed a series type of SQIF amplifier that is compatible to conventional YBa2Cu3O7 (YBCO)technology on bicrystal substrates. We present analytical, numericaland scale modeling as well as first electrical measurementsresults at frequencies up to 10 GHz. The SQIF array consists of 50 loops with randomly distributed areas from 0.5 to 1.5 times of 3x30 m2. We also compared it to the regular array of conventional SQUIDs with the same loop areas. We have additional dc contacts to each 5-th SQUIDs and the SQIFs for control and comparison. Devices are fabricated using Josephson junctions with 3 m width formed in YBCO over 24/24 and 12/12 degrees grain boundaries in yttrium-stabilized zirconia (YSZ) bicrystal substrates.
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| 7. |
- Soloviev, Igor, 1982, et al.
(författare)
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High Voltage Driver for RSFQ Digital Signal Processor
- 2007
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 17:2, s. 470-473
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Tidskriftsartikel (refereegranskat)abstract
- We present an RSFQ based high voltage driver (HVD) developed for the first amplification stage of the hybridsemiconductor-superconductor memory interface for the RSFQdigital signal processor. Implementation of the driver allows to eliminate the impedance mismatch between the RSFQ and standard 50 Ω input of the semiconductor electronics and increases the signal-to-noise ratio to reach reliable signal transmission with sufficiently low bit error rate. This driver can produce output signal of NRZ pulses at 1 Gbit/s speed and 2.4 mV signal level thatis enough to be sensed by LNA on the further amplification stage. The driver was simulated numerically in PSCAN. The driver design is based on the serial stack of 8 SQUIDs with specially configured ground-cuts that form a quasi-coplanar line with 50 Ω impedance. The impedance of the driver has been extracted using 3D EM simulators that accurately take into account multilayer structure and capacitance to the ground. The circuit has been designed for the standard Hypres 4.5 kA/cm2 process. Numericalsimulation results are presented and discussed.
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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. |
- Tolkacheva, Elena, 1980, et al.
(författare)
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Influence of the Bias Supply Lines on the Performace of RSFQ Circuits
- 2005
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 15:2, s. 276-279
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Tidskriftsartikel (refereegranskat)abstract
- Two effects of the bias supply line on the performanceof RSFQ circuits have been studied: inductive coupling between the bias supply line and circuit inductances; effect of the mirrored current in the ground plane. The following results of the study are presented: 3D calculations and experimental measurements of inductivecoupling between parallel and perpendicular microstripsin presence of one and two ground planes; calculated margins dependence on the external magnetic field in RSFQ cell. Bias current density extraction method has been developed and implemented in RSFQ circuit design flow.
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