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Applied Superconductivity, IEEE Transactions on

Issue 3 • Date June 2011

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Displaying Results 1 - 25 of 201
  • Table of contents

    Publication Year: 2011 , Page(s): C1
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  • IEEE Transactions on Applied Superconductivity publication information

    Publication Year: 2011 , Page(s): C2
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  • Table of contents

    Publication Year: 2011 , Page(s): 73 - 81
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  • Blank page

    Publication Year: 2011 , Page(s): 82
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  • ASC 2010 Chair's Introduction

    Publication Year: 2011 , Page(s): 83 - 84
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  • 2010 Conference Organization

    Publication Year: 2011 , Page(s): 85 - 91
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  • The IEEE Council on Superconductivity Awards for Contributions in the Field of Applied Superconductivity (2010)

    Publication Year: 2011 , Page(s): 92 - 101
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  • Integration of Planarized Internally-Shunted Submicron NbN Junctions

    Publication Year: 2011 , Page(s): 102 - 106
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1418 KB) |  | HTML iconHTML  

    NbN-TaN-Nb(Ti)N non-hysteretic SNS Josephson junctions with TaXN barriers tuned through nitrogen content at metal-insulator transition have been produced in a reliable way with characteristic voltage RNIC above 1.5 mV at 9 K. Barriers are typically 7-10 nm thick and Jc in the range 5 to 25 kA/cm-2 making feasible LSI RSFQ ADC circuit integration by using the lithographic tools of the Leti C-MOS platform. Junction tri-layers, NbTiN ground-plane and wiring levels have been reactively sputtered and optimized at 300°C in a reproducible way on 8-inch oxidized silicon wafers. A deep UV stepper combined with SF6 gas mixtures RIE has been used to achieve low spread lithography in junction diameters of 716 nm (3σ ~ 40 nm), of 465 nm (3σ ~ 84 nm) across the 8-inch. A well controlled CMP planarization process has been developed on thick PE-CVD silica layers deposited on each superconducting nitride layer. On-line FIB-SEM observations and electrical characterizations associated to the development of a technology test vehicle demonstrate the feasibility of the complete process. The reliable production of nitrides LSI RSFQ circuits such as ADCs and integrated imagers operating in a relaxed cryogenic environment in the 6-10 K temperature range is foreseen to open new telecoms and medical applications. Moreover, a new MgO-AlN-MgO layered insulating barrier junction is shown to operate above 10 K and will be developed for analog front-end circuit parts. View full abstract»

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  • Magnesium Diboride Flexible Flat Cables for Cryogenic Electronics

    Publication Year: 2011 , Page(s): 107 - 110
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (369 KB) |  | HTML iconHTML  

    Magnesium diboride (MgB2) thin films are a potential alternative to low-temperature superconductors (LTS) due to a higher critical temperature (Tc) of approximately 39 K. The reactive evaporation deposition technique also affords relatively simple growth of MgB2 films on flexible substrates compared to high-temperature superconductors (HTS). We have designed and fabricated a cable architecture consisting of MgB2 traces on flexible yttria-stabilized zirconia (YSZ) compatible with commercially available connectors or direct wirebonds. Key performance metrics such as critical current density (Jc) and Tc are measured and compared. We discuss thermal conductivity and passivation schemes for these cables. View full abstract»

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  • Improved Characteristics of Intrinsically Shunted {\rm Nb/Al}-{\rm AlO}_{x}-{\rm Nb} Josephson Junctions

    Publication Year: 2011 , Page(s): 111 - 114
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB) |  | HTML iconHTML  

    Josephson junctions with non-hysteretic current-voltage characteristics form the basis of most superconducting electronic circuits including RSFQ logic and programmable Josephson voltage standards. In contrast to conventional SIS devices, Nb/Al-AlOx-Nb (SNIS) junctions with an additional comparatively thick Al interlayer and a comparatively thin barrier AlOx are intrinsically shunted at T ≥ 4.2 K . In this contribution, we provide experimental and theoretical arguments proving that this finding is mainly explained by a broad distribution of highly-conductive barrier transparencies with a significant effect from nearly ballistic modes. An additional advantage of the proposed SNIS junctions is possibility to tune the critical voltage value by modifying Nb and/or Al film thicknesses. With observations of wide Shapiro steps up to 1.25 V at 6.3 K we show that this type of Josephson junctions can be successfully used at temperatures above 4.2 K. The presence of well-developed quantized voltage features even at 7.2 K means that Nb/Al-AlOx-Nb devices can successfully operate far above the liquid helium temperature and, in principle, are compatible with two-stage cryocoolers. View full abstract»

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  • {\rm MgB}_{2}/{\rm MgO/MgB}_{2} Josephson Junctions for High-Speed Circuits

    Publication Year: 2011 , Page(s): 115 - 118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (623 KB) |  | HTML iconHTML  

    MgB2/MgO/MgB2 sandwich-type Josephson junctions have been fabricated using MgB2 films grown by hybrid physical-chemical vapor deposition (HPCVD). The MgO barrier and the insulating layer between wiring layers were made by RF magnetron sputtering. The junctions exhibit non-vanishing Jc up to 40 K, the Tc of MgB2. MgB2 wiring is achieved without significantly changing the junction properties. The fabrication and properties of the junctions are described in detail. The I-V curves of the junctions are hysteretic at temperatures below 25 K and are RSJ-like above 25 K. Multiple Andreev reflection was observed, manifested by subgap peaks in the dI/dV-V curves and in good agreement with the theory. The Jc spread (1σ) of 10 junctions on one chip is better than 10%, which is likely due to the defects inside the MgO barrier as identified by transmission electron microscopy. Superconducting circuits made of these junctions may be expected to work at frequencies up to 1 THz or at temperatures over 20 K. View full abstract»

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  • Diffusion Stop-Layers for Superconducting Integrated Circuits and Qubits With Nb-Based Josephson Junctions

    Publication Year: 2011 , Page(s): 119 - 125
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (924 KB) |  | HTML iconHTML  

    New technology for superconductor integrated circuits has been developed and is presented. It employs diffusion stop-layers (DSLs) to protect Josephson junctions (JJs) from interlayer migration of impurities, improve JJ critical current (Ic) targeting and reproducibility, eliminate aging, and eliminate pattern-dependent effects in Ic and tunneling characteristics of Nb/Al/AlOx/Nb junctions in integrated circuits. The latter effects were recently found in Nb-based JJs integrated into multi layered digital circuits. E.g., it was found that Josephson critical current density (Jc) may depend on the JJ's environment, on the type and size of metal layers making contact to niobium base (BE) and counter electrodes (CE) of the junction, and also change with time. Such Jc variations within a circuit reduce circuit performance and yield, and restrict integration scale. This variability of JJs is explained as caused by hydrogen contamination of Nb layers during wafer processing, which changes the height and structural properties of AlOx tunnel barrier. Redistribution of hydrogen impurities between JJ electrodes and other circuit layers by diffusion along Nb wires and through contacts between layers causes long-term drift of Jc. At least two DSLs are required to completely protect JJs from impurity diffusion effects-right below the junction BE and right above the junction CE. The simplest and the most technologically convenient DSLs we have found are thin (from ~3 nm to ~10 nm) layers of Al. They were deposited in-situ under the BE layer, thus forming an Al/Nb/Al/AlOx/Nb penta-layer, and under the first wiring layer to junctions' CE, thus forming an Al/Nb wiring bi-layer. A significant improvement of Jc uniformity on 150-mm wafer has also been obtained along with large improvements in Jc targeting and run-to-run reproducibility. View full abstract»

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  • Investigation of the Role of H in Fabrication-Process- Induced Variations of {\rm Nb}/{\rm Al}/{\rm AlO}_{x}/{\rm Nb} Josephson Junctions

    Publication Year: 2011 , Page(s): 126 - 130
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (537 KB) |  | HTML iconHTML  

    The correct operation and high performance of complex superconducting integrated circuits significantly depend on fabrication-process-induced variations of the Josephson junction critical current Ic. Such variations in Nb/Al/AlOx/Nb junctions were investigated and shown to be dependent on how the junction electrodes are connected to other layers in the integrated circuit, especially the ground plane and the Ti/Pd/Au contact pad. The observed enhancement of Ic and gap voltage over time for junctions with certain wiring connections suggests that the phenomenon is related to the diffusion over time of impurities between the junction electrode and the Ti/Pd/Au pad. Considering the strong affinity of both Nb and Ti to H, a model where H is the main impurity element involved in the diffusion-related phenomenon is presented. The results show that direct wiring to Ti is sufficient to observe Ic variations. The results also suggest that as fabricated, the interface between the junction counter-electrode and the AlOx barrier is already close to or at full H saturation, significantly depressing the Ic by up to 20%, compared to clean Nb junctions. View full abstract»

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  • The Effect of Magnetic Nanoparticles on Inductances for SFQ Device Application

    Publication Year: 2011 , Page(s): 131 - 134
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    The use of magnetic material can improve the performance of a single-flux-quantum device by inducing high self-or mutual inductance, which can reduce the size or increase the sensitivity of the device. We used magnetic nanoparticles as the magnetic material and adopted photoresist patterns with Fe3O4 nanoparticles as a means of inserting nanoparticles into a device. The effect of the nanoparticles was investigated for SQUIDs with photoresist patterns. Analytical estimation of the effect indicated a variation in SQUID inductance of less than 1%, which is in agreement with the experimental results in the absence of external magnetic fields. On the other hand, when external DC magnetic fields were applied, a slight increase in inductance was observed for several SQUIDs. View full abstract»

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  • Measurement of Epitaxial NbN/AlN/NbN Tunnel Junctions With a Low Critical Current Density at Low Temperature

    Publication Year: 2011 , Page(s): 135 - 138
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB) |  | HTML iconHTML  

    Superconducting qubit circuits require high quality low critical current density Josephson tunnel junctions. We have developed high quality epitaxial NbN/AlN/NbN tunnel junctions with critical current density, Jc, ranging from as low as a few A/cm2 to a few tens of kA/cm2. In this work, we measured current-voltage characteristics for junctions with a Jc ~ 32 A/cm2 in the temperature range from 17 mK to above 6.7 K. All the junctions are in good quality and have a high gap voltage (>; 5.5 mV). We found that the junctions' sub-gap resistances were temperature dependent above 2.5 K and saturated at temperatures below 2.5 K. A junction sub-gap leakage current Ir of about 23 pA was measured. The voltage noise power spectral density for 3 junctions with different sizes has been measured at the base temperature of 17 mK with the junctions biased above the gap voltage. The spectral densities clearly show 1/f behavior at low frequency and are proportional to the junction's linear dimension. View full abstract»

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  • Characterization of NbTiN Thin Films Deposited on Various Substrates

    Publication Year: 2011 , Page(s): 139 - 142
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (135 KB) |  | HTML iconHTML  

    Niobium titanium nitride (NbTiN) thin films were deposited on a selection of different substrates to explore the optimum depositing condition of high-quality NbTiN thin films. The NbTiN films deposited on MgO, Al2O3, and fused quartz substrates showed excellent superconducting properties with a high TC of 14.7 K, 14.5 K, 15.2 K, and low resistivity ρ20 K of 55 μΩcm, 116 μΩcm, 78 μΩcm, respectively. The chemical composition, crystal structure, and relationship between superconducting properties and crystal structure were systematically investigated by changing the N2/(Ar+N2) ratio in sputtering gases. The lattice parameter systematically changed as N2/(Ar+N2) ratio was varied. We found that the superconducting properties depend on the lattice parameter, and the film with the best superconducting properties had a lattice parameter of 4.380 Å (on MgO), 4.345 Å (on Al2O3), 4.335 Å (on fused quartz). View full abstract»

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  • Infrared Pulsed Laser Deposition of Niobium Nitride Thin Films

    Publication Year: 2011 , Page(s): 143 - 146
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    We have successfully fabricated superconducting niobium nitride thin films on single crystals of magnesium oxide using a pulsed laser deposition technique where 1064 nm (photon energy ~1.16 eV) laser pulses from an Nd:YAG laser were used for ablation. A correlation between the superconducting transition temperature, the nitrogen base pressure during deposition and the lattice parameter of the produced NbN films was observed. Superconductor-insulator-normal metal junctions fabricated using these NbN films as the superconductor revealed nonlinear electrical characteristics at 4.2 K associated with quasiparticle tunneling. View full abstract»

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  • Evolution of Electrical and Electrodynamic Properties of {\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-{\rm x}} Bicrystal Josephson Junctions With Oxygen Loading

    Publication Year: 2011 , Page(s): 147 - 150
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (306 KB) |  | HTML iconHTML  

    The I-V curves and dynamic resistances Rd (V) of [001]-tilt YBa2Cu3O7-x bicrystal Josephson junctions have been experimentally studied at various levels of oxygen loading. Oxygen content was modified by annealing in ozone atmosphere, in vacuum or in air. Deviations of the IV -curves from those predicted by the RSJC model in the form of additional nonlinearities at the middle and high voltages were found to decrease after enhancement of oxygen content in junctions. Electrodynamic properties of Josephson junctions were analyzed using log-periodic YBa2Cu3O7-x antennas, integrated with the junctions. Fine structures on the IV-curves, related to antenna resonances, were modified with oxygen content due to better antenna-junction coupling and lower electromagnetic losses in YBa2Cu3O7-x film. View full abstract»

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  • Feasibility of a High Temperature Superconductor rf-SQUID Based on Biepitaxial Josephson Junction Technology

    Publication Year: 2011 , Page(s): 151 - 155
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (599 KB) |  | HTML iconHTML  

    Recently, the observation of macroscopic quantum effects in high critical temperature superconductor (HTS) Josephson junctions (JJs) paved the way to the possible use of HTS in quantum hybrid circuits. Dissipation in HTS JJs has been proven to be below expectations, even in junction configurations designed to fully exploit the functionality of a d-wave order parameter symmetry, where low energy quasi-particles can be more harmful for coherence. We report on the design of YBaCuO rf-SQUIDs based on the properties of sub-micron biepitaxial junctions with variable inter face orientation with respect to the order parameters of the two electrodes. The study of the double well potential of such system may offer further insights for a deeper understanding of the dynamics of a HTS Josephson device. The rf-SQUID has been de signed to have independent controls for the barrier height between the wells and for the relative positions of the energy levels in different fluxoid wells. The flux state of the rf-SQUID is readout by an inductively coupled dc-SQUID magnetometer. View full abstract»

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  • Step-Edge Josephson Junctions on Multilayered High Temperature Superconducting Thin Film

    Publication Year: 2011 , Page(s): 156 - 159
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (658 KB) |  | HTML iconHTML  

    Application of Josephson effect in sensors, electronic and metrological devices working at temperature of 77 K requires fabrication of efficient and reproducible high temperature superconducting (HTS) Josephson junctions. In order to enhance the performance of HTS junctions, we introduce multilayered approach to YBCO-based step-edge Josephson junction manufacture. Thin YBCO and multilayered YBCO/NdBCO/YBCO films of a similar thickness ( ~ 210 nm) were grown by a pulsed-laser deposition technique on MgO (100) substrates with artificially created step edge. Large discrepancies of Ic and Rn values were found between these two types of junction. Results of their structural and electrical properties are reported. View full abstract»

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  • Annealing Temperature Effects on {\rm YBCO/LaAlO}_{3} and {\rm YBCO/CeO}_{2}/{\rm Al}_{2}{\rm O}_{3} for Microwave Applications by TFA-MOD

    Publication Year: 2011 , Page(s): 160 - 163
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2830 KB) |  | HTML iconHTML  

    YBa2Cu3O7-x (YBCO) superconducting films can be used for microwave applications due to their low surface resistance. Both LaAlO3 and Al2O3 can be considered as applicable substrates since their excellent properties for the preparation of high-quality YBCO films and for the design of microwave elements. In order to optimize the annealing temperature, the microstructure and properties were investigated for YBCO/LaAlO3 and YBCO/CeO2/r-cut Al2O3 films prepared by trifluoroacetates metal organic deposition (TFA-MOD). The results show that the annealing temperature window is broader for YBCO films on LaAlO3 substrates; while, the window is relative narrower for YBCO films on CeO2/Al2O3 substrates. The reasons were also discussed. The surface resistivity (Rs) was measured for the samples with highest critical current density (Jc). The results will provide useful information about processing effects on YBCO films using TFA-MOD for microwave applications. View full abstract»

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  • Transport Properties of YBCO Nanowires

    Publication Year: 2011 , Page(s): 164 - 167
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (410 KB) |  | HTML iconHTML  

    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. View full abstract»

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  • Intrinsic Josephson Junctions in Bi-2212 Thin Films Fabricated by Metal-Organic Decomposition

    Publication Year: 2011 , Page(s): 168 - 171
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (545 KB) |  | HTML iconHTML  

    We fabricated a mesa 10 μm × 10 μm in area and ~ 150 nm in height on a single grain in a 240-nm Bi2Sr2CaCu2O8+δ/MgO thin-film grown by metal-organic decomposition (MOD) with face-to-face annealing. A multi-branch structure peculiar to intrinsic Josephson junctions (IJJs) was observed in the I-V characteristics of the fabricated mesa, and this structure was characterized by approximately 100 quasiparticle branches with critical current densities of 1 kA/cm2 and voltage-jump intervals of 20 mV. Moreover, the temperature dependence of the critical current was in good agreement with a theoretical result based on c-axis Josephson tunneling in d-wave superconductors. These results imply that the thin films grown by MOD have sufficient quality to fabricate IJJs for practical terahertz applications. View full abstract»

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  • Characterization of {\rm Bi}_{2}{\rm Sr}_{2}{\rm CaCu}_{2}{\rm O}_{8+\delta } Stacks Fabricated by Acid Treatment Process

    Publication Year: 2011 , Page(s): 172 - 175
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (510 KB) |  | HTML iconHTML  

    Bi2Sr2CaCu2O8+δ (Bi-2212) stacks of intrinsic Josephson junctions were fabricated by an acid-treatment process from inside a single crystal. The surrounding acid-treated product is a transparent material, BiOCl. During the process, an optical adhesive (NOA-61) was used to fix a piece of the crystal on a glass substrate and to coat the surface of the sample. The current-voltage characteristics of the stacks at T = 77 K exhibited large hystereses and multiple branches with voltage spacings of approximately 2-3 mV. Under an external microwave field in the frequency range of 2-18 GHz, clear Shapiro steps were observed at voltages with multiples of (h/2e)frf. In addition, the thermal cycling properties of the critical current (Ic) were investigated. No apparent degradation of the Ic was observed during repeated thermal cycling between 300 and 77 K. View full abstract»

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  • Shapiro Step Response of Intrinsic Josephson Junctions With High Critical Currents of {({\rm Bi}_{1-{\rm x}}{\rm Pb}_{\rm x})}_{2}{\rm Sr}_{2}{\rm CaCu}_{2}{\rm O}_{\rm y}

    Publication Year: 2011 , Page(s): 176 - 179
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (195 KB) |  | HTML iconHTML  

    We have studied the response of intrinsic Josephson junctions (IJJs) in cross-shaped samples of (Bi1-xPbx)2Sr2CaCu2Oy (x=0.15) with high critical currents Ic at 4.2 K to injection of microwave with frequencies frf of 2-20 GHz. At the early stage of measurements Josephson vortex flow is induced in the IJJs by supplying high currents to them. After that, by injection of microwave power P to them clear constant voltage steps are successfully observed on their current-voltage characteristics, although their plasma frequency fpl is much higher than frf and they are not resistively shunted. The constant voltage steps appear so as to satisfy the Josephson frequency-voltage relation and behave like Shapiro steps depending on P. Such behavior of steps is well reproduced by numerical simulations on Shapiro step response of JJs with shunt resistivity which is equal to the Josephson-vortex flow resistivity under microwave injection. Consequently, the observed constant voltage steps may be Shapiro steps out of the IJJs with the Josephson-vortex flow resistivity. View full abstract»

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Aims & Scope

IEEE Transactions on Applied Superconductivity contains articles on the applications of superconductivity and other relevant technology.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Britton L. T. Plourde
Syracuse University
bplourde@syr.edu
http://www.phy.syr.edu/~bplourde