| 1. |
- Ruffieux, Silvia, 1990, et al.
(författare)
-
Feedback solutions for low crosstalk in dense arrays of high-T-c SQUIDs for on-scalp MEG
- 2017
-
Ingår i: Superconductor Science & Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 30:5
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetoencephalography (MEG) systems based on a dense array of high critical temperature (high-T-c) superconducting quantum interference devices (SQUIDs) can theoretically outperform a state-of-the-art MEG system. On the way towards building such a multichannel system, we evaluate feedback methods suitable for use in dense high-T-c SQUID arrays where the sensors are in very close proximity to the head (on-scalp MEG). We test on-chip superconducting coils and direct injection of the feedback current into the SQUID loop as alternatives to the wire-wound copper coils commonly used in single-channel high-T-c SQUID-based MEG systems. For the evaluation, we have performed coupling, noise, and crosstalk measurements. We conclude that direct injection is the optimal solution for dense on-scalp MEG as it gives crosstalk below 0.5% even between SQUIDs whose pickup loops are within 0.8 mm of one another. Further, this solution provides sufficient flux coupling without adding additional noise. Finally, it does not compromise the standoff distance, which is important for on-scalp MEG.
|
|
| 2. |
- Xie, Minshu, 1988, et al.
(författare)
-
Improved coupling of nanowire-based high-T-c SQUID magnetometers-simulations and experiments
- 2017
-
Ingår i: Superconductor Science & Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 30:11
-
Tidskriftsartikel (refereegranskat)abstract
- Superconducting quantum interference devices (SQUIDs) based on high critical-temperature superconducting nanowire junctions were designed, fabricated, and characterized in terms of their potential as magnetometers for magnetoencephalography (MEG). In these devices, the high kinetic inductance of junctions and the thin film thickness (50 nm) pose special challenges in optimizing the field coupling. The high kinetic inductance also brings difficulties in reaching a low SQUID noise. To explore the technique for achieving a high field sensitivity, single-layer devices with a directly connected pickup loop and flip-chip devices with an inductively coupled flux transformer using a two-level coupling approach were fabricated and tested. Two-level coupling is an approach designed for flip-chip nanowire-based SQUIDs, in which a washer type SQUID pickup loop is introduced as an intermediate coupling level between the SQUID loop and the flux transformer input coil. The inductances and effective areas of all these devices were simulated. We found that at T = 77 K, flip-chip devices with the two-level coupling approach (coupling coefficient of 0.37) provided the best effective area of 0.46 mm(2) among all the tested devices. With a flux noise level of 55 mu Phi(0) Hz-1/2, the field sensitivity level was 240 fTHz-1/2. This sensitivity is not yet adequate for MEG applications but it is the best level ever reached for nanowire-based high-Tc SQUID magnetometers.
|
|
| 3. |
|
|
| 4. |
- Trabaldo, Edoardo, 1990, et al.
(författare)
-
Electromigration tuning of the voltage modulation depth in YBa2Cu3O7-delta nanowire-based SQUIDs
- 2021
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 34:10
-
Tidskriftsartikel (refereegranskat)abstract
- Oxygen electromigration applied to a YBa2Cu3O7-delta nanowire can be used to tune its electrical properties. Here, we apply electromigration to YBCO nanowire-based superconducting quantum interference devices (SQUIDs) and study its effect on the voltage modulation depth of the devices. Using a dc electromigration current we replenish the oxygen of the weak links, improving the critical current symmetry of the SQUIDs. AC current electromigration is used to reduce the doping level of the weak links, thus reducing their critical current and increasing differential resistance. Both type of electromigration processes are found to improve the SQUIDs performance, although the best results are obtained with ac biased electromigration, which improved the voltage modulations of the SQUIDs by a factor as high as 8. This procedure can be instrumental to fine tune ex-situ the properties of superconducting electronics where a large number of weak links are required.
|
|
| 5. |
- Adamyan, Astghik, 1984, et al.
(författare)
-
Kinetic inductance as a microwave circuit design variable by multilayer fabrication
- 2015
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 28:8
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the development of a reliable NbN/Al/Nb/NbN multilayer fabrication technique for combining design elements with and without kinetic inductance in superconducting microwave circuits. As a proof-of-concept we demonstrate the application of the proposed technique to build a slow microwave propagation line matched to 50 Ω terminals. Fabrication details along with the design and measurements are discussed. At 8 GHz the presented device operates as a dc controllable full-turn phase shifter. We suggest that by exploiting the kinetic inductance as a design variable one can greatly improve operation parameters for a variety of standard microwave designs such as step-impedance filters and resonators.
|
|
| 6. |
- Agulo, Ian Jasper, 1974, et al.
(författare)
-
An array of SIN tunnel junctions as a sensitive thermometer
- 2008
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 21:1, s. 5-
-
Tidskriftsartikel (refereegranskat)abstract
- We have fabricated and measured an array of superconductor-insulator-normal metal (SIN) tunnel junctions for the purpose of using it as a sensitive thermometer. An increase in the temperature responsivity of dV/dT similar to 5 mu V mK(-1) for ten junctions is observed from dV/dT similar to 1 mu V mK(-1) for a single junction. We then used such an array thermometer to measure the temperature stability of the Heliox AC-V cryogen-free refrigerator. We have been able to measure a temperature stability of +/- 250 mu K over a period of 8 h with a temperature resolution of +/- 100 mu K.
|
|
| 7. |
- Arpaia, Riccardo, 1985, et al.
(författare)
-
Highly homogeneous YBCO/LSMO nanowires for photoresponse experiments
- 2014
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 27:4
-
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.
|
|
| 8. |
- Arpaia, Riccardo, 1985, et al.
(författare)
-
Improved noise performance of ultrathin YBCO Dayem bridge nanoSQUIDs
- 2017
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 30:1
-
Tidskriftsartikel (refereegranskat)abstract
- We have fabricated YBa2Cu3O7-delta (YBCO) nano superconducting quantum interference devices (nanoSQUIDs), realized in Dayem bridge configuration, on films with thickness down to 10 nm. The devices, which have not been protected by a Au capping layer during the nanopatterning, show modulations of the critical current as a function of the externally applied magnetic field from 300 mK up to the critical temperature of the nanobridges. The absence of the Au shunting layer and the enhancement of the sheet resistance in ultrathin films lead to very large voltage modulations and transfer functions, which make these nanoSQUIDs highly sensitive devices. Indeed, by using bare YBCO nanostructures, we have revealed an upper limit for the intrinsic white flux noise level S-Phi,w(1/2)
|
|
| 9. |
- Bauch, Thilo, 1972, et al.
(författare)
-
Dynamics of d-wave YBa2Cu3O7-x
- 2007
-
Ingår i: Superconductor Science and Technology. - 0953-2048 .- 1361-6668. ; 20:2, s. S98-S104
-
Konferensbidrag (refereegranskat)abstract
- The predominant d-wave pairing symmetry in high temperature superconductors leads to an unconventional current phase relation in Josephson junctions. This circumstance may induce new effects in the dynamics of dc SQUIDs. In this contribution we report on the measurements of the dependence of the SQUID Josephson current on the external magnetic field taken at very low temperatures, down to 20 mK. Different grain boundaries have been fabricated by using the biepitaxial and the bicrystal technique. Some of the effects which are induced by a nonsinusoidal current phase relation can be clearly identified in the dynamics of the SQUIDs. The experimental data are also compared with theoretical simulations taking into account the inductance of the loop. The data show that, in specific conditions, a non-negligible inductance of the loop can induce effects similar to an unconventional current phase relation, with a pronounced second harmonic sin(2) term. This fact has to be taken into account when designing d-wave SQUIDs for quantum circuitry.
|
|
| 10. |
- Bezuglyi, Eugene, et al.
(författare)
-
Multiparticle tunnelling in diffusive superconducting junctions
- 2007
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 20:6, s. 529-541
-
Tidskriftsartikel (refereegranskat)abstract
- We formulate a theoretical framework to describe multiparticle current transport in planar superconducting tunnel junctions with diffusive electrodes. The approach is based on the direct solving of quasiclassical Keldysh-Green function equations for nonequilibrium superconductors, and consists of a combination of circuit theory analysis and improved perturbation expansion. The theory predicts a much greater scaling parameter for the subharmonic gap structure of the tunnel current in diffusive junctions compared to the one in ballistic junctions and mesoscopic constrictions with the same barrier transparency. © IOP Publishing Ltd.
|
|
