Effect of in-plane line defects on field-tuned superconductor-insulator transition behavior in homogeneous thin film

Field-tuned superconductor-insulator transition (FSIT) behavior in 2D isotropic and homogeneous thin films is usually accompanied by a nonvanishing critical resistance at low $T$. It is shown that, in a 2D film including line defects paralle to each other but with random positions perpendicular to them, the (apparent) critical resistance in low $T$ limit vanishes, as in the 1D quantum superconducting (SC) transition, under a current parallel to the line defects. This 1D-like critical resistive behavior is more clearly seen in systems with weaker point disorder and may be useful in clarifying whether the true origin of FSIT behavior in the parent superconductor is the glass fluctuation or the quantum SC fluctuation. As a by-product of the present calculation, it is also pointed out that, in 2D films with line-like defects with a long but {\it finite} correlation length parallel to the lines, a quantum metallic behavior intervening the insulating and SC ones appears in the resistivity curves.Comment: 16 pages, 14 figure

Production method of nickel electrode

A nickel electrode having improved charging efficiency, an increased coefficient of discharging utilization, and large capacity is disclosed. Nickel hydroxide or nickel oxide is retained in a porous nickel substrate which is immersed in an aqueous solution of cobalt acetate with a pH 4.0 to 6.8. The electrode thus obtained is then immersed in an alkaline solution or heated to change cobalt acetate into cobalt hydroxide or cobalt oxide whereby the surface of nickel active material is covered with cobalt crystals and alloying of cobalt and nickel is promoted at the same time

Giant tunnel magnetoresistance and high annealing stability in CoFeB/MgO/CoFeB magnetic tunnel junctions with synthetic pinned layer

We investigated the relationship between tunnel magnetoresistance (TMR) ratio and the crystallization of CoFeB layers through annealing in magnetic tunnel junctions (MTJs) with MgO barriers that had CoFe/Ru/CoFeB synthetic ferrimagnet pinned layers with varying Ru spacer thickness (tRu). The TMR ratio increased with increasing annealing temperature (Ta) and tRu, reaching 361% at Ta = 425C, whereas the TMR ratio of the MTJs with pinned layers without Ru spacers decreased at Ta over 325C. Ruthenium spacers play an important role in forming an (001)-oriented bcc CoFeB pinned layer, resulting in a high TMR ratio through annealing at high temperatures.Comment: 10 pages, 5 figures, submitted to Applied Physics Letter

Superconducting transition in disordered granular superconductors in magnetic fields

Motivated by a recent argument that the superconducting (SC) transition field of three-dimensional (3D) disordered superconductors with granular structure in a nonzero magnetic field should lie above $H_{c2}(0)$ in low $T$ limit, the glass transition (or, in 2D, crossover) curve $H_g(T)$ of disordered quantum Josephson junction arrays is examined by incorporating SC fluctuations. It is found that the glass transition or crossover in the granular materials can be described on the same footing as the vortex-glass (VG) transition in amorphous-like (i.e., nongranular) materials. In most of 3D granular systems, the vanishing of resistivity upon cooling should occur even above $H_{c2}(0)$, while the corresponding sharp drop of the resistivity in 2D case may appear only below $H_{c2}$ as a result of an enhanced quantum fluctuation.Comment: Accepted for publication in Phys. Rev. B. The content of sec.3 in v.2 was removed from here and presented more extensively in a separate paper (cond-mat/0606522) where the argument of nonsuperconducting vortex-glass in cond-mat/0512432 is shown to be fals

Numerical Computation of Thermoelectric and Thermomagnetic Effects

Phenomenological equations describing the Seebeck, Hall, Nernst, Peltier, Ettingshausen, and Righi-Leduc effects are numerically solved for the temperature, electric current, and electrochemical potential distributions of semiconductors under magnetic field. The results are compared to experiments.Comment: 4 pages, 7 figures. Submitted to Proceedings of XVII International Conference on Thermoelectrics (ICT98), 1998 Nagoya, Japa

Evidence regarding clinical use of microvolt T-wave alternans [Accuracy of microvolt T-wave alternans testing]

Background: Microvolt T-wave alternans (MTWA) testing in many studies has proven to be a highly accurate predictor of ventricular tachyarrhythmic events (VTEs) in patients with risk factors for sudden cardiac death (SCD) but without a prior history of sustained VTEs (primary prevention patients). In some recent studies involving primary prevention patients with prophylactically implanted cardioverter-defibrillators (ICDs), MTWA has not performed as well. Objective: This study examined the hypothesis that MTWA is an accurate predictor of VTEs in primary prevention patients without implanted ICDs, but not of appropriate ICD therapy in such patients with implanted ICDs. Methods: This study identified prospective clinical trials evaluating MTWA measured using the spectral analytic method in primary prevention populations and analyzed studies in which: (1) few patients had implanted ICDs and as a result none or a small fraction (≤15%) of the reported end point VTEs were appropriate ICD therapies (low ICD group), or (2) many of the patients had implanted ICDs and the majority of the reported end point VTEs were appropriate ICD therapies (high ICD group). Results: In the low ICD group comprising 3,682 patients, the hazard ratio associated with a nonnegative versus negative MTWA test was 13.6 (95% confidence interval [CI] 8.5 to 30.4) and the annual event rate among the MTWA-negative patients was 0.3% (95% CI: 0.1% to 0.5%). In contrast, in the high ICD group comprising 2,234 patients, the hazard ratio was only 1.6 (95% CI: 1.2 to 2.1) and the annual event rate among the MTWA-negative patients was elevated to 5.4% (95% CI: 4.1% to 6.7%). In support of these findings, we analyzed published data from the Multicenter Automatic Defibrillator Trial II (MADIT II) and Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) trials and determined that in those trials only 32% of patients who received appropriate ICD therapy averted an SCD. Conclusion: This study found that MTWA testing using the spectral analytic method provides an accurate means of predicting VTEs in primary prevention patients without implanted ICDs; in particular, the event rate is very low among such patients with a negative MTWA test. In prospective trials of ICD therapy, the number of patients receiving appropriate ICD therapy greatly exceeds the number of patients who avert SCD as a result of ICD therapy. In trials involving patients with implanted ICDs, these excess appropriate ICD therapies seem to distribute randomly between MTWA-negative and MTWA-nonnegative patients, obscuring the predictive accuracy of MTWA for SCD. Appropriate ICD therapy is an unreliable surrogate end point for SCD