We report on measurements of supercurrents through the half-metallic ferromagnet CrO 2 grown on hexagonal Al 2 O 3 ͑sapphire͒. The current was observed to flow over a distance of 700 nm between two superconducting amorphous Mo 70 Ge 30 electrodes which were deposited on the CrO 2 film. The critical current I c increases as function of decreasing temperature. Upon applying an in-plane magnetic field, I c goes through a maximum at the rather high field of 80 mT. We believe this to be a long-range proximity effect in the ferromagnet, carried by odd-frequency pairing correlations. DOI: 10.1103/PhysRevB.82.100501 PACS number͑s͒: 74.45.ϩc, 72.25.Mk, 74.50.ϩr, 75.70.Cn The proximity-effect arising when a ferromagnet ͑F͒ is brought into contact with a conventional superconductor ͑S͒, is generally assumed to be small. The superconducting pair correlations decay rapidly inside the magnet since the phase coherence between the two spins forming the singlet Cooper pair is broken up by the exchange field h ex . In the dirty limit, the decay length F ϰ 1 / ͱ h ex is no more than 10 nm even for a weak ferromagnet. To compare, in a normal ͑N͒ metal the dephasing is due to temperature fluctuations with a decay length N ϰ 1 / ͱ k B T, which can reach microns at low T. Longrange proximity ͑LRP͒ effects in ferromagnets would be possible with spin-triplet Cooper pairs, since they do not suffer decay through h ex , but the orbital p symmetry required by the Pauli principle makes such the pair strongly susceptible to potential scattering by defects in the material. However, under the principle of odd-frequency pairing, also s symmetry is possible, 1,2 and the existence of odd-frequency s-wave triplet pairs could lead to LRP effects in dirty ferromagnets. To produce such triplets in the magnet, the singlet Cooper pair on the S side of the interface needs to sample an inhomogeneous magnetization on the F side, 1,2 or in a variant, spin mixing and magnetic disorder at the interface.3 Fully spin-polarized magnets ͑also called half-metallic ferromagnet͒ are particularly interesting since in such materials triplet correlations cannot be broken by spin-flip scattering and the decay length is set by thermal dephasing only.Subsequently, experimental observations indicating LRP effects were made by Sosnin et al., 4 who found supercurrents flowing in ferromagnetic Ho wires with lengths up to 150 nm using an Andreev interferometer geometry; and by Keizer et al., 5 who found supercurrents induced in half-metallic ferromagnetic CrO 2 , when superconducting electrodes of NbTiN with separations up to 1 m were placed on unstructured films. Even for normal metals this can be considered a very long range. No other experiments were reported for quite some time but this is now rapidly changing. In the last few months, reports came out on Josephson junctions where thin PdNi layers 6 or Ho layers 7 ͑providing magnetic inhomogeneity͒ were combined with Co layers and where no decay of the value of the Josephson current was found up to a thickness of 3...

There is strong experimental evidence that the superconductor Sr2RuO4 has a chiral p-wave order parameter. This symmetry does not require that the associated gap has nodes, yet specific heat, ultrasound and thermal conductivity measurements indicate the presence of nodes in the superconducting gap structure of Sr2RuO4. Theoretical scenarios have been proposed to account for the existence of deep minima or accidental nodes (minima tuned to zero or below by material parameters) within a p-wave state. Other scenarios propose chiral d-wave and f -wave states, with horizontal and vertical line nodes, respectively. To elucidate the nodal structure of the gap, it is essential to know whether the lines of nodes (or minima) are vertical (parallel to the tetragonal c axis) or horizontal (perpendicular to the c axis). Here, we report thermal conductivity measurements on single crystals of Sr2RuO4 down to 50 mK for currents parallel and perpendicular to the c axis. We find that there is substantial quasiparticle transport in the T = 0 limit for both current directions. A magnetic field H immediately excites quasiparticles with velocities both in the basal plane and in the c direction. Our data down to Tc/30 and down to Hc2/100 show no evidence that the nodes are in fact deep minima. Relative to the normal state, the thermal conductivity of the superconducting state is found to be very similar for the two current directions, from H = 0 to H = Hc2. These findings show that the gap structure of Sr2RuO4 consists of vertical line nodes. This rules out a chiral d-wave state. Given that the c-axis dispersion (warping) of the Fermi surface in Sr2RuO4 varies strongly from surface to surface, the small a − c anisotropy suggests that the line nodes are present on all three sheets of the Fermi surface. If imposed by symmetry, vertical line nodes would be inconsistent with a p-wave order parameter for Sr2RuO4. To reconcile the gap structure revealed by our data with a p-wave state, a mechanism must be found that produces accidental line nodes in Sr2RuO4.

No abstract

We report measurements of long ranged supercurrents through ferromagnetic and fully spinpolarized CrO2 deposited on TiO2 substrates. In earlier work, we found supercurrents in films grown on sapphire but not on TiO2. Here we employed a special contact arrangement, consisting of a Ni/Cu sandwich between the film and the superconducting amorphous Mo70Ge30 electrodes. The distance between the contacts was almost a micrometer, and we find the critical current density to be significantly higher than found in the films deposited on sapphire. We argue this is due to spin mixing in the Ni/Cu/CrO2 layer structure, which is helpful in the generation of the odd-frequency spin triplet correlations needed to carry the supercurrent.

Background: Surgical mortality data are collected routinely in high-income countries, yet virtually no low-or middle-income countries have outcome surveillance in place. The aim was prospectively to collect worldwide mortality data following emergency abdominal surgery, comparing findings across countries with a low, middle or high Human Development Index (HDI).Methods: This was a prospective, multicentre, cohort study. Self-selected hospitals performing emergency surgery submitted prespecified data for consecutive patients from at least one 2-week interval during July to December 2014. Postoperative mortality was analysed by hierarchical multivariable logistic regression.

Efforts have been ongoing to establish superconducting spintronics utilizing ferromagnet/superconductor heterostructures. Previously reported devices are based on spin-singlet superconductors (SSCs), where the spin degree of freedom is lost. Spin-polarized supercurrent induction in ferromagnetic metals (FMs) is achieved even with SSCs, but only with the aid of interfacial complex magnetic structures, which severely affect information imprinted to the electron spin. Use of spin-triplet superconductors (TSCs) with spin-polarizable Cooper pairs potentially overcomes this difficulty and further leads to novel functionalities. Here, we report spin-triplet superconductivity induction into a FM SrRuO3 from a leading TSC candidate Sr2RuO4, by fabricating microscopic devices using an epitaxial SrRuO3/Sr2RuO4 hybrid. The differential conductance, exhibiting Andreev-reflection features with multiple energy scales up to around half tesla, indicates the penetration of superconductivity over a considerable distance of 15 nm across the SrRuO3 layer without help of interfacial complex magnetism. This demonstrates potential utility of FM/TSC devices for superspintronics.

No abstract

It is becoming gradually clear that it is possible to induce superconducting correlations in ferromagnets by generating so-called odd-frequency triplet Cooper pairs, which have two equal (rather than opposite) spins. Half-metallic ferromagnets (HMF) such as CrO 2 are of special interest here since the presence of only a single spin band and no possibility for spin flip scattering can lead to very long lengths over which a supercurrent is induced. Early experiments with superconducting (S) contacts on CrO 2 films found supercurrents over distances of up to a micrometer. The generation of triplet correlations is assumed to involve inhomogeneous magnetization or disordered magnetic moments in the ferromagnet or at the interface, and a major question still is how this is brought about in the S/CrO 2 case. Here we report on experiments in which CrO 2 thin films are grown on two different substrates, TiO 2 and sapphire (single crystalline Al 2 O 3 ). Using amorphous Mo 70 Ge 30 superconducting contacts, we find supercurrents can flow in films grown on sapphire, but we have not been able yet to induce supercurrents in films grown on TiO 2 . We discuss this in terms of the differences in film morphology and the magnetic anisotropy for both film systems. We also show that the characteristic behavior of the clean S/HMF interface is a jump at the superconducting transition temperature of the resistance of the device to larger values.