Nonlinear detection of spin currents in graphene with non-magnetic electrodes

Nature Physics (Impact Factor: 20.6). 04/2012; 8(4). DOI: 10.1038/nphys2219
Source: arXiv

ABSTRACT The abilities to inject and detect spin carriers are fundamental for
research on transport and manipulation of spin information. Pure
electronic spin currents have been recently studied in nanoscale
electronic devices using a non-local lateral geometry, both in metallic
systems and in semiconductors. To unlock the full potential of
spintronics we must understand the interactions of spin with other
degrees of freedom. Such interactions have been explored recently, for
example, by using spin Hall or spin thermoelectric effects. Here we
present the detection of non-local spin signals using non-magnetic
detectors, through an as-yet-unexplored nonlinear interaction between
spin and charge. In analogy to the Seebeck effect, where a heat current
generates a charge potential, we demonstrate that a spin current in a
paramagnet leads to a charge potential, if the conductivity is energy
dependent. We use graphene as a model system to study this effect, as
recently proposed. The physical concept demonstrated here is generally
valid, opening new possibilities for spintronics.

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    ABSTRACT: We propose a theoretical approach to detect spin currents by converting them into measurable charge currents or potentials in a three-terminal zigzag graphene nanoribbon (ZR) junction. By means of the Keldysh Green's function technique, we demonstrate that when pure spin currents are flowing into the middle region of a nonmagnetic n-doped/normal/p-doped (n/N/p) ZR junction or a ferromagnetic/normal/ferromagnetic (F/N/F) ZR junction, nonzero charge currents could be induced in the ZR terminals due to the combination of the spin-dependent chemical potential splitting and the valley-valve effect in the even-chain ZR. The induced charge currents can be affected by some system parameters such as the Fermi energy, the tunneling strength and the magnetization. It is also shown that the spin-polarized direction of the spin currents can be deduced from the charge currents in the F/N/F ZR junction. Our proposal may provide a useful way to indirectly detect pure spin currents in a graphene-based spin device.
    Journal of Physics Condensed Matter 12/2012; 25(3):035303. · 2.22 Impact Factor
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    ABSTRACT: Motivated by recent experiments [ I. J. Vera-Marun, V. Ranjan and B. J. van Wees Nat. Phys. 8 313 (2012)], we formulate a nonlinear theory of spin transport in quantum coherent conductors. We show how a mesoscopic constriction with energy-dependent transmission can convert a spin current injected by a spin accumulation into an electric signal, relying neither on magnetic nor exchange fields. When the transmission through the constriction is spin independent, the spin-charge coupling is nonlinear, with an electric signal that is quadratic in the accumulation. We estimate that gated mesoscopic constrictions have a sensitivity that allows to detect accumulations much smaller than a percent of the Fermi energy.
    Physical review. B, Condensed matter 12/2011; 85(24). · 3.66 Impact Factor
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    ABSTRACT: We propose an approach to detect spin currents in an even zigzag graphene nanoribbon (ZR) junction, based on the peculiar intervalley selection rule in the ribbon when only zero-energy modes are involved in transport. Spatial spin separation arises from the bipolar property of the undoped ZR and opposite pseudoparities of electrons in the conduction and valence bands, and does not involve any magnetic field or spin orbit interaction. A measurable fully spin-polarized charge current or potential can thus be converted from either coherent or incoherent spin resources. Our findings may shed light on making spintronics devices based on graphene nanoribbons.
    Physical review. B, Condensed matter 08/2012; · 3.66 Impact Factor

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