| 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.
|
|
| 11. |
- Bezuglyi, Eugene, et al.
(författare)
-
Nonequilibrium and relaxation effects in tunnel superconducting junctions
- 2017
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 30:2
-
Tidskriftsartikel (refereegranskat)abstract
- The specific property of a planar tunnel junction with thin-film diffusive plates and long enough leads is an essential enhancement of its transmission coefficient compared to the bare transparency of the tunnel barrier [1, 2]. In voltage-biased junctions, this creates favorable conditions for strong nonequilibrium of quasiparticles in the junction plates and leads, produced by multiparticle tunneling. We study theoretically the interplay between the nonequilibrium and relaxation processes in such junctions and found that nonequilibrium in the leads noticeably modifies the currentvoltage characteristic at eV > 2D, especially the excess current, whereas strong diffusive relaxation restores the result of the classical tunnel model. At eV > 2D, the diffusive relaxation decreases the peaks of the multiparticle currents. The inelastic relaxation in the junction plates essentially suppresses the n-particle currents (n > 2) by the factor n for odd and n 2 for even n. The results may be important for the problem of decoherence in Josephsonjunction based superconducting qubits.
|
|
| 12. |
- Boikov, Iouri, 1949, et al.
(författare)
-
Strain enhanced anisotropy of in-plane resistivity of YBa2Cu3O7-delta films
- 2013
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 26:11
-
Tidskriftsartikel (refereegranskat)abstract
- Highly bi-axially stressed, thin epitaxial films of YBa2Cu3O7-delta were deposited on mismatched, orthorhombic (001) YAlO3 substrates. Strain may be used to enhance anisotropy and affect spin and charge ordering in cuprate superconductors. The resistivity was anisotropic along the a and b axes and the ratio rho(a)/rho(b) approximate to 2 agreed well with that for untwinned single crystals. rho(a)(T), but not rho(b)(T), peaked sharply at a temperature closely above the superconducting transition temperature, while the latter estimated from rho(b)(T) exceeded the one determined from rho(a)(T). The height of the peak Delta rho(a) in rho(a)(T) decreased with increased bias current and applied magnetic field. The behavior may be explained by partly relaxed regions, preferably aligned along the b axis, but may also depend upon spin/charge ordering.
|
|
| 13. |
- Cedergren, Karin, 1975, et al.
(författare)
-
Biepitaxial YBa2Cu3O7-x 0-pi Josephson junctions
- 2010
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 23:3, s. Article Number: 034027-
-
Tidskriftsartikel (refereegranskat)abstract
- We present measurements performed on YBa2Cu3O7-x '0' and '0-pi' Josephson junctions fabricated using the biepitaxial technique with SrTiO3 as substrate and CeO2 as seed layer. Measurements of the critical current as a function of external magnetic field clearly show complementary behavior of the two kinds of junctions. Our results unambiguously show that the d-wave nature of the order parameter dominates the current transport across the junctions despite the faceting on the microscale along the grain boundary line.
|
|
| 14. |
- Chang, H. H., et al.
(författare)
-
Growth and characterization of superconducting beta-FeSe type iron chalcogenide nanowires
- 2014
-
Ingår i: Superconductor Science & Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 27:2
-
Tidskriftsartikel (refereegranskat)abstract
- We have grown highly crystalline beta-FeSe type iron chalcogenide nanowires (NWs) by annealing thin film that is prepared by a pulsed laser deposition method. Three kinds of NWs with compositions of Fe0.8Se, Fe0.88Se0.32Te0.68 and Fe0.88Te0.91S0.09 have been prepared and carefully characterized by a high-resolution transmission electron microscope (HRTEM). The NWs reveal ideal tetragonal structure with crystal growth along the [100] direction. Energy dispersive spectroscopy (EDS) studies and HRTEM images show the NWs to have good compositional uniformity, except for the existence of a thin layer of oxide on the surface. No superconducting transition was observed in the FeSex NWs, which is possibly caused by Fe deficiency. The other two types of NWs show relatively higher and sharper superconducting transitions than their bulk counterparts. Interestingly, a resistive transition tail is observed in the NWs with diameter smaller than 100 nm, which might originate from a phase slip process in the quasi-one-dimensional system. The success in producing these high quality NWs provides a new avenue for better understanding the origin of superconductivity in beta-FeSe type iron chalcogenides.
|
|
| 15. |
- Chang, H. H., et al.
(författare)
-
The vortex state of FeSe1-xTex superconducting thin films
- 2011
-
Ingår i: Superconductor Science & Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 24:10
-
Tidskriftsartikel (refereegranskat)abstract
- We report the vortex dynamics of tellurium substituted FeSe1-xTex superconducting thin films. The electric field versus current density (E-J) curve for films with low Te substitution is still governed by the thermally activated flux flow model at temperatures as low as 0.5T(C)(offset). In contrast, we clearly observed a vortex liquid-glass transition in films with high Te substitution. The E-J curves of these samples fit nicely to the scaling relations based on the 3D vortex glass theory. Our results reveal an enhancement of the vortex pinning as more Te content is introduced, which probably originates from the excess Fe at the interstitial site.
|
|
| 16. |
- Chang, H. H., et al.
(författare)
-
Weak localization in FeSe1-xTex superconducting thin films
- 2012
-
Ingår i: Superconductor Science & Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 25:3
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the magneto-resistivity (MR) of FeSe1-xTex superconducting films on MgO substrate. The MR of pure FeSe and slightly Te-substituted films demonstrates regular Lorentz-type magnetic field dependence, MR similar to B-2. In highly Te-substituted samples, however, negative MR contribution due to the weak-localization effect gradually dominates at low temperature, which is consistent with the evolution of the temperature dependence of resistivity from a metallic to a weakly semiconductor-like behavior. Furthermore, the negative MR weakens and turns positive as temperature approaches the superconducting transition temperature, which is evidence for the Maki-Thompson correction in the weak-localization regime. The experimental data can be described very well by the weak-localization theory with the existence of scattering by some magnetic moments. The fitting parameters demonstrate that disorder most likely comes from the excess iron.
|
|
| 17. |
- Intiso, Samuel, 1978, et al.
(författare)
-
Rapid single-flux-quantum circuits for low noise mK operation
- 2006
-
Ingår i: Superconductor Science and Technology. - 0953-2048 .- 1361-6668. ; 19:5
-
Tidskriftsartikel (refereegranskat)abstract
- Rapid single-flux-quantum (RSFQ) technology has been proposed as control electronics for superconducting quantum bits because of the material and working temperature compatibility. In this work, we consider practical aspects of RSFQ circuit design for low noise low power operation. At the working temperature of 20 mK and operational frequency of 2 GHz, dissipated power per junction is reduced to 25 pW by using 6 νA critical current junctions available at the Hypres and VTT low Jc fabrication process. To limit phonon temperature to 30 mK, a maximum of 40 junctions can be placed on a 5 mm × 5 mm chip. Electron temperature in resistive shunts of Josephson junctions is minimized by use of cooling fins, giving minimum electron temperatures of about 150 mK for the Hypres process and 70 mK for the VTT process.
|
|
| 18. |
- Körber, R., et al.
(författare)
-
SQUIDs in biomagnetism: A roadmap towards improved healthcare
- 2016
-
Ingår i: Superconductors Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 29:11
-
Tidskriftsartikel (refereegranskat)abstract
- Globally, the demand for improved health care delivery while managing escalating costs is a major challenge. Measuring the biomagnetic fields that emanate from the human brain already impacts the treatment of epilepsy, brain tumours and other brain disorders. This roadmap explores how superconducting technologies are poised to impact health care. Biomagnetism is the study of magnetic fields of biological origin. Biomagnetic fields are typically very weak, often in the femtotesla range, making their measurement challenging. The earliest in vivo human measurements were made with room-temperature coils. In 1963, Baule and McFee (1963 Am. Heart J. 55 95-6) reported the magnetic field produced by electric currents in the heart ('magnetocardiography'), and in 1968, Cohen (1968 Science 161 784-6) described the magnetic field generated by alpha-rhythm currents in the brain ('magnetoencephalography'). Subsequently, in 1970, Cohen et al (1970 Appl. Phys. Lett. 16 278-80) reported the recording of a magnetocardiogram using a Superconducting QUantum Interference Device (SQUID). Just two years later, in 1972, Cohen (1972 Science 175 664-6) described the use of a SQUID in magnetoencephalography. These last two papers set the scene for applications of SQUIDs in biomagnetism, the subject of this roadmap. The SQUID is a combination of two fundamental properties of superconductors. The first is flux quantization - the fact that the magnetic flux Φ in a closed superconducting loop is quantized in units of the magnetic flux quantum, Φ0 ≡ h/2e, ≈ 2.07 × 10-15 Tm2 (Deaver and Fairbank 1961 Phys. Rev. Lett. 7 43-6, Doll R and Nabauer M 1961 Phys. Rev. Lett. 7 51-2). Here, h is the Planck constant and e the elementary charge. The second property is the Josephson effect, predicted in 1962 by Josephson (1962 Phys. Lett. 1 251-3) and observed by Anderson and Rowell (1963 Phys. Rev. Lett. 10 230-2) in 1963. The Josephson junction consists of two weakly coupled superconductors separated by a tunnel barrier or other weak link. A tiny electric current is able to flow between the superconductors as a supercurrent, without developing a voltage across them. At currents above the 'critical current' (maximum supercurrent), however, a voltage is developed. In 1964, Jaklevic et al (1964 Phys. Rev. Lett. 12 159-60) observed quantum interference between two Josephson junctions connected in series on a superconducting loop, giving birth to the dc SQUID. The essential property of the SQUID is that a steady increase in the magnetic flux threading the loop causes the critical current to oscillate with a period of one flux quantum. In today's SQUIDs, using conventional semiconductor readout electronics, one can typically detect a change in Φ corresponding to 10-6 Φ0 in one second. Although early practical SQUIDs were usually made from bulk superconductors, for example, niobium or Pb-Sn solder blobs, today's devices are invariably made from thin superconducting films patterned with photolithography or even electron lithography. An extensive description of SQUIDs and their applications can be found in the SQUID Handbooks (Clarke and Braginski 2004 Fundamentals and Technology of SQUIDs and SQUID Systems vol I (Weinheim, Germany: Wiley-VCH), Clarke and Braginski 2006 Applications of SQUIDs and SQUID Systems vol II (Weinheim, Germany: Wiley-VCH)). The roadmap begins (chapter 1) with a brief review of the state-of-the-art of SQUID-based magnetometers and gradiometers for biomagnetic measurements. The magnetic field noise referred to the pick-up loop is typically a few fT Hz-1/2, often limited by noise in the metallized thermal insulation of the dewar rather than by intrinsic SQUID noise. The authors describe a pathway to achieve an intrinsic magnetic field noise as low as 0.1 fT Hz-1/2, approximately the Nyquist noise of the human body. They also descibe a technology to defeat dewar noise. Chapter 2 reviews the neuroscientific and clinical use of magnetoencephalography (MEG), by far the most widespread application of biomagnetism with systems containing ty ically 300 sensors cooled to liquid-helium temperature, 4.2 K. Two important clinical applications are presurgical mapping of focal epilepsy and of eloquent cortex in brain-tumor patients. Reducing the sensor-to-brain separation and the system noise level would both improve spatial resolution. The very recent commercial innovation that replaces the need for frequent manual transfer of liquid helium with an automated system that collects and liquefies the gas and transfers the liquid to the dewar will make MEG systems more accessible. A highly promising means of placing the sensors substantially closer to the scalp for MEG is to use high-transition-temperature (high-T c) SQUID sensors and flux transformers (chapter 3). Operation of these devices at liquid-nitrogen temperature, 77 K, enables one to minimize or even omit metallic thermal insulation between the sensors and the dewar. Noise levels of a few fT Hz-1/2 have already been achieved, and lower values are likely. The dewars can be made relatively flexible, and thus able to be placed close to the skull irrespective of the size of the head, potentially providing higher spatial resolution than liquid-helium based systems. The successful realization of a commercial high-T c MEG system would have a major commercial impact. Chapter 4 introduces the concept of SQUID-based ultra-low-field magnetic resonance imaging (ULF MRI) operating at typically several kHz, some four orders of magnitude lower than conventional, clinical MRI machines. Potential advantages of ULF MRI include higher image contrast than for conventional MRI, enabling methodologies not currently available. Examples include screening for cancer without a contrast agent, imaging traumatic brain injury (TBI) and degenerative diseases such as Alzheimer's, and determining the elapsed time since a stroke. The major current problem with ULF MRI is that its signal-to-noise ratio (SNR) is low compared with high-field MRI. Realistic solutions to this problem are proposed, including implementing sensors with a noise level of 0.1 fT Hz-1/2. A logical and exciting prospect (chapter 5) is to combine MEG and ULF MRI into a single system in which both signal sources are detected with the same array of SQUIDs. A prototype system is described. The combination of MEG and ULF MRI allows one to obtain structural images of the head concurrently with the recording of brain activity. Since all MEG images require an MRI to determine source locations underlying the MEG signal, the combined modality would give a precise registration of the two images; the combination of MEG with high-field MRI can produce registration errors as large as 5 mm. The use of multiple sensors for ULF MRI increases both the SNR and the field of view. Chapter 6 describes another potentially far-reaching application of ULF MRI, namely neuronal current imaging (NCI) of the brain. Currently available neuronal imaging techniques include MEG, which is fast but has relatively poor spatial resolution, perhaps 10 mm, and functional MRI (fMRI) which has a millimeter resolution but is slow, on the order of seconds, and furthermore does not directly measure neuronal signals. NCI combines the ability of direct measurement of MEG with the spatial precision of MRI. In essence, the magnetic fields generated by neural currents shift the frequency of the magnetic resonance signal at a location that is imaged by the three-dimensional magnetic field gradients that form the basis of MRI. The currently achieved sensitivity of NCI is not quite sufficient to realize its goal, but it is close. The realization of NCI would represent a revolution in functional brain imaging. Improved techniques for immunoassay are always being sought, and chapter 7 introduces an entirely new topic, magnetic nanoparticles for immunoassay. These particles are bio-funtionalized, for example with a specific antibody which binds to its corresponding antigen, if it is present. Any resulting changes in the properties of the nanoparticles are detected with a SQUID. For liquid-phase detection, there are three ba ic methods: AC susceptibility, magnetic relaxation and remanence measurement. These methods, which have been successfully implemented for both in vivo and ex vivo applications, are highly sensitive and, although further development is required, it appears highly likely that at least some of them will be commercialized. © 2016 IOP Publishing Ltd.
|
|
| 19. |
- Ovsyannikov, Gennady, 1948, et al.
(författare)
-
Proximity effect and electron transport in oxide hybrid heterostructures with superconducting/magnetic interfaces
- 2011
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 24:5, s. Art. no. 055012-
-
Tidskriftsartikel (refereegranskat)abstract
- We report on electron transport in oxide heterostructures with superconducting/magnetic (S/M) thin film interfaces. The investigated hybrid mesa-heterostructures consist of a cuprate superconductor, a nonsuperconducting cuprate (antiferromagnetic) or manganite (ferromagnetic) interlayer with thickness d(M) = 5-50 nm and a conventional superconductor (Nb). The superconducting critical current (I-C) with a critical current density j(c) = 10(3) A cm(-2) (for d(M) = 10 nm) and a characteristic voltage ICRN = 100-200 mu V (RN is normal resistance) are observed at liquid helium temperature for a CaXSr1-XCuO2 antiferromagnetic cuprate interlayer with a thickness of d(M) = 10-50 nm. The superconducting current-phase relation of heterostructures deviates from the regular sine type, demonstrating a second harmonic component. These hybrid heterostructures with S/M interfaces show unusually high sensitivity to external magnetic fields. When substituting the cuprate interlayer by a manganite film, no critical current was observed although the manganite interlayer was made several times thinner (down to d(M)
|
|
| 20. |
- Rafique, Raihan, 1978, et al.
(författare)
-
Optimization of high frequency flip-chip interconnects for digital superconducting circuits
- 2006
-
Ingår i: Superconductor Science and Technology. - 0953-2048 .- 1361-6668. ; 15:5, s. S354-S361
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents results of optimization of Multi-Chip-Module (MCM) contact pads and driver circuitry for gigabit chip-to-chip communication. Optimization has been done using 3D Electromagnetic (EM) simulations of flip-chip contacts and time domain simulations of drivers and receivers. A single optimized flip-chip contact has signal refection of less than -20 dB for up to 503 GHz bandwidth. The MCM data link with optimized SFQ driver, receivers and two MCM contact has operational margins on global bias current of +-30% at 30 Gbit/s speed and can operate at maximum 113 Gbit/s of operational speed. High bandwidth transmission requires realization of an advanced flip-chip process with small dimension of contact pads (less 30 micro meter) and small hight of bumps in the order of 2 micro meter. Current processes with about 7 micro meter hight of the bumps requires application of Double Flux Quantum (DFQ) driver. The data link with DFQ driver was also simulated. It has operational margins on global bias current of +-30% at 30 Gbit/s, however the maximum speed of operation is 61 Gbit/s. Several test structures have been designed for measurements signal re°ection, bit error rate (BER) and operational margins of the data link.
|
|
| 21. |
- Rafique, Raihan, 1978, et al.
(författare)
-
Optimization of Superconducting Microstrip Interconnects for Rapid Single-Flux-Quantum Circuits
- 2005
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 18:8, s. 1065-1072
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the issues related to the optimization ofsuperconducting passive interconnects are discussed. The results of the microwave optimization of bends, vias connections and crossings of the superconducting microstrip lines (SMSL) are reported. The optimum design of the SMSL cross gives more than 95% of transmission and can be well used in two busses cross design with up to 14 signal wires. The results have been confirmed by time-domain simulations and measurements.
|
|
| 22. |
- Stockhausen, A., et al.
(författare)
-
Adjustment of self-heating in long superconducting thin film NbN microbridges
- 2012
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 25:3
-
Tidskriftsartikel (refereegranskat)abstract
- The self-heating in long superconducting microbridges made from thin NbN films deposited on top of high silicon mesa structures was studied by analyzing the hysteresis current density j(H). We observed a more than twofold decrease of j(H) with increase in the ratio of the height of the Si mesa, h, to the width of the microbridge, W, from 0 to 24. We describe our experimental results using one-dimensional thermal balance equations taking into account disordered matter in our thin NbN films and limitations imposed on the phonon mean free path by the width of the Si mesa. In the framework of this model we obtain a good agreement between theory and experiment over a wide temperature range from 4.2 K up to the critical temperature T-C for all h/W ratios.
|
|
| 23. |
- Yurgens, Avgust, 1959, et al.
(författare)
-
Temperature distribution in a stack of intrinsic Josephson junctions with their CuO-plane electrodes oriented perpendicular to supporting substrate
- 2011
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 24:1, s. 015003-
-
Tidskriftsartikel (refereegranskat)abstract
- We numerically study Joule heating in a THz emitter made of Bi2Sr2CaCu2O{8+δ} (Bi2212) single crystal with its CuO planes oriented perpendicular to supporting substrate. The single crystal is glued to the substrate by a layer of PMMA. The electrical current is applied in the c-axis direction across many intrinsic Josephson junctions (IJJ's) in Bi2212. The calculations show that the internal temperature increases to an acceptable 10–20 K only above the bath temperature for a Joule power density of ~ 10^5 W /cm^3 typical for experiments on THz emission from IJJ's. This makes the suggested geometry promising for boosting the output power of the emitter.
|
|
| 24. |
- Andersson, Eric, 1992, et al.
(författare)
-
Fabrication and electrical transport characterization of high quality underdoped YBa2Cu3O7-δ nanowires
- 2020
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 33:6
-
Tidskriftsartikel (refereegranskat)abstract
- We present the fabrication and electrical transport characterization of underdoped YBa2Cu3O7-δnanowires. The nanowires have been realized without any protective capping layer and theyshow transport properties similar to those of the parent thin film, demonstrating that they havenot been damaged by the nanopatterning. The current-voltage characteristics of the underdopednanowires show large hysteretic voltage switching at the critical current, in contrast to theflux-flow like characteristics of optimally doped nanostructures, indicating the formation of aself-stabilizing hot spot. These results open up new possibilities for using the underdopednanowires as single photon detectors and for exploring the underdoped side of the YBa2Cu3O7-δphase diagram at the nanoscale.
|
|
| 25. |
- Antipov, S., et al.
(författare)
-
Improved bandwidth of a 2THz hot-electron bolometer heterodyne mixer fabricated on sapphire with a GaN buffer layer
- 2019
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 32:7
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the signal-to-noise and gain bandwidth of a niobium nitride (NbN) hot-electron bolometer (HEB) mixer at 2 THz fabricated on a sapphire substrate with a GaN buffer layer. Two mixers with different DC properties and geometrical dimensions were studied and they demonstrated very close bandwidth performance. The signal-to-noise bandwidth is increased to 8 GHz in comparison to the previous results, obtained without a buffer-layer. The data were taken in a quasi-optical system with the use of the signal-to-noise method, which is close to the signal levels used in actual astrophysical observations. We find an increase of the gain bandwidth to 5 GHz. The results indicate that prior results obtained on a substrate of crystalline GaN can also be obtained on a conventional sapphire substrate with a few micron MOCVD-deposited GaN buffer-layer.
|
|
