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The generation, manipulation and detection of spin-polarized electrons in nanostructures define the main challenges of spin-based electronics 1 . Amongst the different approaches for spin generation and manipulation, spin-orbit coupling, which couples the spin of an electron to its momentum, is attracting considerable interest. In a spin-orbit-coupled system a nonzero spincurrent is predicted in a direction perpendicular to the applied electric field, giving rise to a "spin Hall effect" 2,3,4 . Consistent with this effect, electrically-induced spin polarization was recently detected by optical techniques at the edges of a semiconductor channel 5 and in two-dimensional electron gases in semiconductor heterostructures 6,7 . Here we report electrical measurements of the spin-Hall effect in a diffusive metallic conductor, using a ferromagnetic electrode in combination with a tunnel barrier to inject a spin-polarized current. In our devices, we observe an induced voltage that results exclusively from the conversion of the injected spin current into charge imbalance through the spin Hall effect. Such a voltage is proportional to the component of the injected spins that is perpendicular to the plane defined by the spin current direction and the voltage probes. These experiments reveal opportunities for efficient spin detection without the need for magnetic materials, which could lead to useful spintronics devices that integrate information processing and data storage.The spin Hall effect (SHE), which was first described by Dyakonov and Perel 2,3 and more recently by Hirsch 4 , was proposed to occur in paramagnetic materials as a consequence of the spin-orbit interaction. In analogy to the standard Hall effect, the SHE refers to the generation of a pure spin current transverse to an applied electric field that results in an accompanying spin imbalance in the system. These early theoretical studies considered an extrinsic 2,3,4,8 SHE originating from an asymmetric scattering for spin-up and spin-down electrons. It was pointed out that, after scattering off an impurity, there is a spin-dependent probability difference in the electron trajectories which generates the spin imbalance. In the recently introduced intrinsic 9,10 SHE, spin imbalance is expected to occur even in the absence of scattering as a result of the band structure.Several experimental schemes have been proposed to electrically detect the extrinsic SHE in metals 4,8,11,12 . However, these schemes are difficult to implement. Spinrelated phenomena such as anisotropic magnetoresistance (AMR) in ferromagnetic (FM) electrodes, spin dependent interface scattering, or standard and anomalous Hall effects could render the SHE signal unobservable. We use the measurement scheme in Fig. 1 to study the SHE isolated from such spurious phenomena.It is natural to expect that, if a charge-current induces a transverse spin-imbalance through the spin-

The behaviour of traditional electronic devices can be understood in terms of the classical diffusive motion of electrons. As the size of a device becomes comparable to the electron coherence length, however, quantum interference between electron waves becomes increasingly important, leading to dramatic changes in device properties. This classical-to-quantum transition in device behaviour suggests the possibility for nanometer-sized electronic elements that make use of quantum coherence. Molecular electronic devices are promising candidates for realizing such device elements because the electronic motion in molecules is inherently quantum mechanical and it can be modified by well defined chemistry. Here we describe an example of a coherent molecular electronic device whose behaviour is explicitly dependent on quantum interference between propagating electron waves-a Fabry-Perot electron resonator based on individual single-walled carbon nanotubes with near-perfect ohmic contacts to electrodes. In these devices, the nanotubes act as coherent electron waveguides, with the resonant cavity formed between the two nanotube-electrode interfaces. We use a theoretical model based on the multichannel Landauer-Büttiker formalism to analyse the device characteristics and find that coupling between the two propagating modes of the nanotubes caused by electron scattering at the nanotube-electrode interfaces is important.