The recent observation of superconductivity with critical temperatures (T c ) up to 55 K in the pnictide RFeAsO 1−x F x , where R is a lanthanide, marks the first discovery of a noncopper-oxide-based layered high-T c superconductor 1-3 . It has raised the suspicion that these new materials share a similar pairing mechanism to the cuprate superconductors, as both families exhibit superconductivity following charge doping of a magnetic parent material. In this context, it is important to follow the evolution of the microscopic magnetic properties of the pnictides with doping and hence to determine whether magnetic correlations coexist with superconductivity. Here, we present a muon spin rotation study on SmFeAsO 1−x F x , with x = 0-0.30 that shows that, as in the cuprates, static magnetism persists well into the superconducting regime. This analogy is quite surprising as the parent compounds of the two families have rather different magnetic ground states: itinerant spin density wave for the pnictides contrasted with the MottHubbard insulator in the cuprates. Our findings therefore suggest that the proximity to magnetic order and associated soft magnetic fluctuations, rather than strong electronic correlations in the vicinity of a Mott-Hubbard transition, may be the key ingredients of high-T c superconductors.Similar to the cuprates, the pnictide high-critical-temperature (T c ) superconductors (HTSCs) have a layered structure comprising alternating FeAs and LaO sheets, with the Fe arranged on a square lattice 1 . Theoretical calculations predict a quasi-twodimensional electronic structure, with LaO layers that mainly act as blocking layers and metallic FeAs layers that are responsible for superconductivity [4][5][6] , although these are multiband superconductors with up to five FeAs-related bands crossing the Fermi level [4][5][6][7] . Like the copper-oxide HTSCs, the superconducting state in the pnictides emerges on charge doping a magnetic parent compound [8][9][10] , with indications that the maximal T c occurs just as magnetism disappears [11][12][13] . The last point may well be of great significance, as the parent compounds in the two families are very different. For the pnictides, there are strong indications that they are itinerant systems with magnetism arising from a nesting-induced spin density wave (SDW). This is in contrast to the cuprates, where it is well established that the mother compounds are 'charge transfer insulators', where strongly repulsive electronic correlations yield an insulating and antiferromagnetic ground state despite a half-filled conduction band. It is therefore of great importance to obtain further insight into the differences and similarities of the pnictide and cuprate HTSCs. A particularly important question is how magnetism and superconductivity evolve on electron doping. In this context, muon spin rotation (μSR) is an ideal technique as it provides microscopic information corresponding to the bulk of a sample and there is a substantial body of μSR data that has been colle...

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Electronic devices that use the spin degree of freedom hold unique prospects for future technology. The performance of these 'spintronic' devices relies heavily on the efficient transfer of spin polarization across different layers and interfaces. This complex transfer process depends on individual material properties and also, most importantly, on the structural and electronic properties of the interfaces between the different materials and defects that are common to real devices. Knowledge of these factors is especially important for the relatively new field of organic spintronics, where there is a severe lack of suitable experimental techniques that can yield depth-resolved information about the spin polarization of charge carriers within buried layers of real devices. Here, we present a new depth-resolved technique for measuring the spin polarization of current-injected electrons in an organic spin valve and find the temperature dependence of the measured spin diffusion length is correlated with the device magnetoresistance.R ecently great efforts have been undertaken to use the spin degree of freedom in electronic devices. These activities are fuelled by the potential prospects of spin-electronic (or 'spintronic') devices for example in terms of increased processing speed and integration, non-volatility, reduced power consumption, multifunctionality and their suitability for quantum computing 1 . The most common method for using the spin in devices is based on the alignment of the electron spin ('up' or 'down') relative to either a reference magnetic field or the magnetization orientation of a ferromagnetic layer. Device operation normally proceeds with measuring a quantity such as the electrical current that depends on how the degree of spin alignment is transferred across the device. The so-called 'spin valve' is a prominent example of such a spin-enabled device that has already revolutionized hard-drive read heads and magnetic memory 1 . The efficient transfer of spin polarization in real device structures remains one of the most difficult challenges in spintronics, because it is dependent on more than just the properties of the individual materials that comprise the device.Recently 2,3 , the use of organic materials in spintronics has become of significant interest, primarily owing to their ease and small cost of processing and electronic and structural flexibility. Furthermore, the extremely long spin coherence times found in organic materials offer considerable advantages over other materials 3 . This favourable property is related to two factors, first the weak spin-orbit coupling of light elements such as carbon and second to the small nuclear hyperfine interaction 4,5 . The latter arises because the electron transport in π-conjugated molecules is normally confined to molecular states, delocalized to the carbon rings, the predominant isotope of which, 12 C, has zero nuclear spin 4 .A common way to measure spin diffusion is based on time-resolved optical techniques, where spin-polarized charge carrie...

With infrared ellipsometry and transport measurements we investigated the electrons at the interface between LaAlO3 and SrTiO3. We obtained a sheet carrier concentration of N(s) approximately = 5-9x10(13) cm(-2), an effective mass of m*=3.2+/-0.4m(e), and a strongly frequency dependent mobility. The latter are similar as in bulk SrTi(1-x)Nb(x)O3 and therefore suggestive of polaronic correlations. We also determined the vertical concentration profile which has a strongly asymmetric shape with a rapid initial decay over the first 2 nm and a pronounced tail that extends to about 11 nm.

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