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

The abilities to inject and detect spin carriers are fundamental for research on transport and manipulation of spin information(1,2). 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 semiconductors(4). 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(5-7) or spin thermoelectric effects(6,8,9). 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 effect(10), 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(11) as a model system to study this effect, as recently proposed(12). The physical concept demonstrated here is generally valid, opening new possibilities for spintronics.