Electrical Spin Injection in Multi-Wall carbon NanoTubes with transparent ferromagnetic contacts

We report on electrical spin injection measurements on MWNTs . We use a ferromagnetic alloy Pd$_{1-x}$Ni$_{x}$ with x $\approx$ 0.7 which allows to obtain devices with resistances as low as 5.6 $k\Omega$ at 300 $K$. The yield of device resistances below 100 $k\Omega$, at 300 $K$, is around 50%. We measure at 2 $K$ a hysteretic magneto-resistance due to the magnetization reversal of the ferromagnetic leads. The relative difference between the resistance in the antiparallel (AP) orientation and the parallel (P) orientation is about 2%.Comment: submitted to APL version without figures version with figures available on http://www.unibas.ch/phys-meso

0-pi oscillations in nanostructured Nb/Fe/Nb Josephson junctions

The physics of the $\pi$ phase shift in ferromagnetic Josephson junctions may enable a range of applications for spin-electronic devices and quantum computing. We investigate transitions from ``0'' to ``$\pi$'' states in Nb/Fe/Nb Josephson junctions by varying the Fe barrier thickness from 0.5 nm to 5.5 nm. From magnetic measurements we estimate for Fe a magnetic dead layer of about 1.1 nm. By fitting the characteristic voltage oscillations with existing theoretical models we extrapolate an exchange energy of 256 meV, a Fermi velocity of $1.98 \times 10^5$ m/s and an electron mean free path of 6.2 nm, in agreement with other reported values. From the temperature dependence of the $I_CR_N$ product we show that its decay rate exhibits a nonmonotonic oscillatory behavior with the Fe barrier thickness.Comment: 7 pages, 5 figures, accepted for publication in Eur. Phys. J.

Photon mediated interaction between distant quantum dot circuits

Engineering the interaction between light and matter is an important goal in the emerging field of quantum opto-electronics. Thanks to the use of cavity quantum electrodynamics architectures, one can envision a fully hybrid multiplexing of quantum conductors. Here, we use such an architecture to couple two quantum dot circuits . Our quantum dots are separated by 200 times their own size, with no direct tunnel and electrostatic couplings between them. We demonstrate their interaction, mediated by the cavity photons. This could be used to scale up quantum bit architectures based on quantum dot circuits or simulate on-chip phonon-mediated interactions between strongly correlated electrons

Magnetic properties of Ruddlesden-Popper phases Sr3−x_{3-x}Yx_{x}(Fe1.25_{1.25}Ni0.75_{0.75})O7−δ_{7-\delta}: A combined experimental and theoretical investigation

We present a comprehensive study of the magnetic properties of Sr$_{3-x}$Y$_{x}$(Fe$_{1.25}$Ni$_{0.75}$)O$_{7-\delta}$ ($0 \leq x \leq 0.75$). Experimentally, the magnetic properties are investigated using superconducting quantum interference device (SQUID) magnetometry and neutron powder diffraction (NPD). This is complemented by the theoretical study based on density functional theory as well as the Heisenberg exchange parameters. Experimental results show an increase in the N\'eel temperature ($T_N$) with the increase of Y concentrations and O occupancy. The NPD data reveals all samples are antiferromagnetically ordered at low temperatures, which has been confirmed by our theoretical simulations for the selected samples. Our first-principles calculations suggest that the 3D magnetic order is stabilized due to finite inter-layer exchange couplings. The latter give rise to a finite inter-layer spin correlations which disappear above the $T_N$

Adaptive epidemic dissemination as a finite-horizon optimal stopping problem

Wireless ad hoc networks are characterized by their limited capabilities and their routine deployment in unfavorable environments. This creates the strong requirement to regulate energy expenditure. We present a scheme to regulate energy cost through optimized transmission scheduling in a noisy epidemic dissemination environment. Building on the intrinsically cross-layer nature of the adaptive epidemic dissemination process, we strive to deliver an optimized mechanism, where energy cost is regulated without compromising the network infection. Improvement of data freshness and applicability in routing are also investigated. Extensive simulations are used to support our proposal

Planar SFS Josephson Junctions Made by Focused Ion Beam Etching

Superconductor-Ferromagnet-Superconductor (S-F-S) Josephson junctions were fabricated by making a narrow cut through a S-F double layer using direct writing by Focused Ion Beam (FIB). Due to a high resolution (spot size smaller than 10 nm) of FIB, junctions with a small separation between superconducting electrodes ($\leq$ 30 nm) can be made. Such a short distance is sufficient for achieving a considerable proximity coupling through a diluted CuNi ferromagnet. We have successfully fabricated and studied S-F-S (Nb-CuNi-Nb) and S-S'-S (Nb-Nb/CuNi-Nb) junctions. Junctions exhibit clear Fraunhofer modulation of the critical current as a function of magnetic field, indicating good uniformity of the cut. By changing the depth of the cut, junctions with the $I_c R_n$ product ranging from 0.5 mV to $\sim 1\mu$V were fabricated.Comment: 5 pages, 5 figures, presentation at EUCAS-2003, to be published in Physica

Engineered binding to erythrocytes induces immunological tolerance to E. coli asparaginase.

Antigen-specific immune responses to protein drugs can hinder efficacy and compromise safety because of drug neutralization and secondary clinical complications. We report a tolerance induction strategy to prevent antigen-specific humoral immune responses to therapeutic proteins. Our modular, biomolecular approach involves engineering tolerizing variants of proteins such that they bind erythrocytes in vivo upon injection, on the basis of the premise that aged erythrocytes and the payloads they carry are cleared tolerogenically, driving the deletion of antigen-specific T cells. We demonstrate that binding the clinical therapeutic enzyme Escherichia coli l-asparaginase to erythrocytes in situ antigen-specifically abrogates development of antibody titers by >1000-fold and extends the pharmacodynamic effect of the drug 10-fold in mice. Additionally, a single pretreatment dose of erythrocyte-binding asparaginase tolerized mice to multiple subsequent doses of the wild-type enzyme. This strategy for reducing antigen-specific humoral responses may enable more effective and safer treatment with therapeutic proteins and drug candidates that are hampered by immunogenicity

Effect of d-f hybridization on the Josephson current through Eu-chalcogenides

A superconducting ring with a pi junction made from superconductor/ferromagnetic-metal/superconductor (S-FM-S) exhibits a spontaneous current without an external magnetic field in the ground state. Such pi ring provides so-called quiet qubit that can be efficiently decoupled from the fluctuation of the external field. However, the usage of the FM gives rise to strong Ohmic dissipation. Therefore, the realization of pi junctions without FM is expected for qubit applications. We theoretically consider the possibility of the pi coupling for S/Eu-chalcogenides/S junctions based on the d-f Hamiltonian. By use of the Green's function method we found that pi junction can be formed in the case of the finite d-f hybridization between the conduction d and the localized f electrons.Comment: 4 pages, 4 figure