We have measured a long-range supercurrent in Josephson junctions containing Co (a strong ferromagnetic material) when we insert thin layers of either PdNi or CuNi weakly-ferromagnetic alloys between the Co and the two superconducting Nb electrodes. The critical current in such junctions hardly decays for Co thicknesses in the range of 12-28 nm, whereas it decays very steeply in similar junctions without the alloy layers. The long-range supercurrent is controllable by the thickness of the alloy layer, reaching a maximum for a thickness of a few nm. These experimental observations provide strong evidence for induced spin-triplet pair correlations, which have been predicted to occur in superconducting/ferromagnetic hybrid systems in the presence of certain types of magnetic inhomogeneity.

We have measured with a tunnel probe the energy distribution function of Landau quasiparticles in metallic diffusive wires connected to two reservoir electrodes, with an applied bias voltage. The distribution function in the middle of a 1.5-mm-long wire resembles the half sum of the Fermi distributions of the reservoirs. The distribution functions in 5-mm-long wires are more rounded, due to interactions between quasiparticles during the longer diffusion time across the wire. From the scaling of the data with the bias voltage, we find that the scattering rate between two quasiparticles varies aś 22 , where´is the energy transferred. [S0031-9007(97)04367-6]

We have extracted the phase coherence time τ φ of electronic quasiparticles from the low field magnetoresistance of weakly disordered wires made of silver, copper and gold. In samples fabricated using our purest silver and gold sources, τ φ increases as T −2/3 when the temperature T is reduced, as predicted by the theory of electron-electron interactions in diffusive wires. In contrast, samples made of a silver source material of lesser purity or of copper exhibit an apparent saturation of τ φ starting between 0.1 and 1 K down to our base temperature of 40 mK. By implanting manganese impurities in silver wires, we show that even a minute concentration of magnetic impurities having a small Kondo temperature can lead to a quasi saturation of τ φ over a broad temperature range, while the resistance increase expected from the Kondo effect remains hidden by a large background. We also measured the conductance of Aharonov-Bohm rings fabricated using a very pure copper source and found that the amplitude of the h/e conductance oscillations increases strongly with magnetic field. This set of experiments suggests that the frequently observed "saturation" of τ φ in weakly disordered metallic thin films can be attributed to spin-flip scattering from extremely dilute magnetic impurities, at a level undetectable by other means. I. MOTIVATIONSThe time τ φ during which the quantum coherence of an electron is maintained is of fundamental importance in mesoscopic physics. The observability of many phenomena specific to this field relies on a long enough phase coherence time. 1 Amongst these are the weak localization correction to the conductance (WL), the universal conductance fluctuations (UCF), the Aharonov-Bohm (AB) effect, persistent currents in rings, the proximity effect near the interface between a superconductor and a normal metal, and others. Hence it is crucial to find out what mechanisms limit the quantum coherence of electrons.In metallic thin films, at low temperature, electrons experience mostly elastic collisions from sample boundaries, defects of the ion lattice and static impurities in the metal. These collisions do not destroy the quantum coherence of electrons. Instead they can be pictured as resulting from a static potential on which the diffusivelike electronic quantum states are built.What limits the quantum coherence of electrons are inelastic collisions. These are collisions with other electrons through the screened Coulomb interaction, with phonons, and also with extrinsic sources such as magnetic impurities or two level systems in the metal. Whereas above about 1 K electron-phonon interactions are known to be the dominant source of decoherence, 2 electron-electron interactions are expected to be the leading inelastic process at lower temperatures in samples without extrinsic sources of decoherence. 3 The theory of electron-electron interactions in the diffusive regime was worked out in the early 1980's (for a review see 4 ). It predicts a power law divergence of τ φ when the temperature T goes to zero....

We study current-driven magnetization switching in nanofabricated Ni(84)Fe(16)/Cu/Ni(84)Fe16 trilayers at 295 and 4.2 K. The shape of the hysteretic switching diagram at low magnetic field changes with temperature. The reversible behavior at higher fields involves two phenomena, a threshold current for magnetic excitations closely correlated with the switching current, and a peak in differential resistance characterized by telegraph noise, with an average period that decreases exponentially with current and shifts with temperature. We interpret both static and dynamic results at 295 and 4.2 K in terms of thermal activation over a potential barrier, with a current-dependent effective magnetic temperature.