Visualizing supercurrents in ferromagnetic Josephson junctions with various arrangements of 0 and \pi segments

Josephson junctions with ferromagnetic barrier can have positive or negative critical current depending on the thickness $d_F$ of the ferromagnetic layer. Accordingly, the Josephson phase in the ground state is equal to 0 (a conventional or 0 junction) or to $\pi$ ($\pi$ junction). When 0 and $\pi$ segments are joined to form a "0-$\pi$ junction", spontaneous supercurrents around the 0-$\pi$ boundary can appear. Here we report on the visualization of supercurrents in superconductor-insulator-ferromagnet-superconductor (SIFS) junctions by low-temperature scanning electron microscopy (LTSEM). We discuss data for rectangular 0, $\pi$, 0-$\pi$, 0-$\pi$-0 and 20 \times 0-$\pi$ junctions, disk-shaped junctions where the 0-$\pi$ boundary forms a ring, and an annular junction with two 0-$\pi$ boundaries. Within each 0 or $\pi$ segment the critical current density is fairly homogeneous, as indicated both by measurements of the magnetic field dependence of the critical current and by LTSEM. The $\pi$ parts have critical current densities $j_c^\pi$ up to 35\units{A/cm^2} at T = 4.2\units{K}, which is a record value for SIFS junctions with a NiCu F-layer so far. We also demonstrate that SIFS technology is capable to produce Josephson devices with a unique topology of the 0-$\pi$ boundary.Comment: 29 pages, 8 figure

Interference patterns of multifacet 20x(0-pi-) Josephson junctions with ferromagnetic barrier

We have realized multifacet Josephson junctions with periodically alternating critical current density (MJJs) using superconductor-insulator-ferromagnet-superconductor heterostructures. We show that anomalous features of critical current vs. applied magnetic field, observed also for other types of MJJs, are caused by a non-uniform flux density (parallel to the barrier) resulting from screening currents in the electrodes in the presence of a (parasitic) off-plane field component.Comment: submitted to PR

Noise and conversion properties of Y-Ba-Cu-O Josephson mixers at operating temperatures above 20 K

We have measured the noise performance and conversion efficiency of Y-Ba-Cu-O bicrystal Josephson mixers at operating temperatures between 20 and 60 K and at operating frequencies around 90 GHz. A double-sideband mixer noise temperature of about 1600 K and a conversion efficiency of -10 dB at 20 K operating temperature has been measured using the Y-factor method. The absorbed local oscillator power was in the range of 10 nW. The dependence of the mixer performance on the normalized frequency Omega and the fluctuation parameter Gamma has been studied. In accordance with the resistively shunted junction model, the experimental data show the presence of excess noise. The temperature dependence of the mixer noise temperature can be explained by the variation of the linewidth of the Josephson oscillations with the operating temperature. (C) 2000 American Institute of Physics. [S0003-6951(00)00113-3]

Velocity Distributions of Granular Gases with Drag and with Long-Range Interactions

We study velocity statistics of electrostatically driven granular gases. For two different experiments: (i) non-magnetic particles in a viscous fluid and (ii) magnetic particles in air, the velocity distribution is non-Maxwellian, and its high-energy tail is exponential, P(v) ~ exp(-|v|). This behavior is consistent with kinetic theory of driven dissipative particles. For particles immersed in a fluid, viscous damping is responsible for the exponential tail, while for magnetic particles, long-range interactions cause the exponential tail. We conclude that velocity statistics of dissipative gases are sensitive to the fluid environment and to the form of the particle interaction.Comment: 4 pages, 3 figure

Far-from-equilibrium Ostwald ripening in electrostatically driven granular powders

We report the first experimental study of cluster size distributions in electrostatically driven granular submonolayers. The cluster size distribution in this far-from-equilibrium process exhibits dynamic scaling behavior characteristic of the (nearly equilibrium) Ostwald ripening, controlled by the attachment and detachment of the "gas" particles. The scaled size distribution, however, is different from the classical Wagner distribution obtained in the limit of a vanishingly small area fraction of the clusters. A much better agreement is found with the theory of Conti et al. [Phys. Rev. E 65, 046117 (2002)] which accounts for the cluster merger.Comment: 5 pages, to appear in PR

Magnetic interference patterns in 0-Pi SIFS Josephson junctions: effects of asymmetry between 0 and Pi regions

We present a detailed analysis of the dependence of the critical current I_c on the magnetic field B of 0, Pi, and 0-Pi superconductor-insulator-ferromagnet-superconductor Josephson junctions. I_c(B) of the 0 and Pi junction closely follows a Fraunhofer pattern, indicating a homogeneous critical current density j_c(x). The maximum of I_c(B) is slightly shifted along the field axis, pointing to a small remanent in-plane magnetization of the F-layer along the field axis. I_c(B) of the 0-Pi junction exhibits the characteristic central minimum. I_c however has a finite value here, due to an asymmetry of j_c in the 0 and Pi part. In addition, this I_c(B) exhibits asymmetric maxima and bumped minima. To explain these features in detail, flux penetration being different in the 0 part and the Pi part needs to be taken into account. We discuss this asymmetry in relation to the magnetic properties of the F-layer and the fabrication technique used to produce the 0-Pi junctions

Characterization of Anti-Cancer Activities of Violacein: Actions on Tumor Cells and the Tumor Microenvironment

Natural products have been shown to serve as promising starting points for novel anti cancer drugs. In this study, the anti-cancer activities of the purple compound violacein, initially isolated from Chromobacterium violaceum, were investigated. To highlight the crucial role of the tumor microenvironment on the effectiveness of cancer therapies, this study includes effects on macrophages as prototypic cells of the microenvironment in addition to the investigation of tumor-centric activities. Using 2D and 3D cell culture models, automated live-cell microscopy, and biochemical analyses, violacein was demonstrated to inhibit tumor cell proliferation and migration. The violacein-triggered tumor cell death was further associated with caspase 3-like activation and ATP release. Stimuli released from dead cells resulted in inflammatory activation of macrophages, as shown by NF-kB reporter cell assays, macrophage morphology, and gene expression analysis. Moreover, macrophages deficient in the inflammasome component Nlrp3 were found to be significantly less sensitive towards treatment with violacein and doxorubicin. Taken together, this study provides new insights into the biological activity of violacein against cancer. In addition, the in vitro data suggest immunogenic features of induced cell death, making violacein an interesting candidate for further studies investigating the compound as an inducer of immunogenic cell death

Textures in experimentally deformed olivine aggregates: the effects of added water and melt

Abstract. The texture development in experimentally sheared aggregates of olivine was monitored as a function of increased water content and added melt. In dry samples, an alignment of {010} with the shear plane and <100> and <001> with the shear direction, respectively, was observed, consistent with intracrystalline glide on the (010) [100] an

From Fully Strained to Relaxed: Epitaxial Ferroelectric Al_1-xSc_xN for III-N Technology

The recent emergence of wurtzite-type nitride ferroelectrics such as Al1-xScxN has paved the way for the introduction of all-epitaxial, all-wurtzite-type ferroelectric III-N semiconductor heterostructures. This paper presents the first in-depth structural and electrical characterization of such an epitaxial heterostructure by investigating sputter deposited Al1-xScxN solid solutions with x between 0.19 and 0.28 grown over doped n-GaN. The results of detailed structural investigations on the strain state and the initial unit-cell polarity with the peculiarities observed in the ferroelectric response are correlated. Among these, a Sc-content dependent splitting of the ferroelectric displacement current into separate peaks, which can be correlated with the presence of multiple strain states in the Al1-xScxN films is discussed. Unlike in previously reported studies on ferroelectric Al1-xScxN, all films thicker than 30 nm grown on the metal (M)-polar GaN template feature an initial multidomain state. The results support that regions with opposed polarities in as-grown films do not result as a direct consequence of the in-plane strain distribution, but are rather mediated by the competition between M-polar epitaxial growth on an M-polar template and a deposition process that favors nitrogen (N)-polar growth

Low-voltage operation of metal-ferroelectric-insulator-semiconductor diodes incorporating a ferroelectric polyvinylidene fluoride copolymer Langmuir-Blodgett film

We report the electrical characteristics of metal-ferroelectric-insulator-semiconductor structures, where the ferroelectric layer is a Langmuir-Blodgett film of a copolymer of 70% vinylidene fluoride and 30% trifluoroethylene. The 36-nm thick copolymer films were deposited on thermally oxidized (10 nm SiO2) p-type silicon and covered with a gold gate electrode. Polarization-field hysteresis loops indicate polarization switching in the polymer film. The device capacitance shows hysteresis when cycling the applied voltage between ±3 V, exhibiting a zero-bias on/off capacitance ratio of over 3:1 and a symmetric memory window 1 V wide, with little evidence of bias that can arise from traps in the oxide. Model calculations are in good agreement with the data and show that film polarization was not saturated. The capacitance hysteresis vanishes above the ferroelectric- paraelectric transition temperature, showing that it is due to polarization hysteresis. The retention time of both the on and off states was approximately 15 min at room temperature, possibly limited by leakage or by polarization instability in the unsaturated film. These devices provide a basis for nonvolatile data storage devices with fast nondestructive readout