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

Abstract

The degree to which an electrical current is spin polarized is usually determined by how easily it travels across an interface with a magnetic contact. By using nonlinear interactions between spin and charge in graphene, the polarization of spin currents can be measured without magnetic contacts. The abilities to inject and detect spin carriers are fundamental for research on transport and manipulation of spin information1,2. Pure electronic spin currents have been recently studied in nanoscale electronic devices using a non-local lateral geometry, both in metallic systems 3 and in semiconductors4. 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 Hall5,6,7 or spin thermoelectric effects6,8,9. 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 effect10, 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 graphene11 as a model system to study this effect, as recently proposed12. The physical concept demonstrated here is generally valid, opening new possibilities for spintronics.