Direct Demonstration of Decoupling of Spin and Charge Currents in Nanostructures

The notion of decoupling of spin and charge currents is one of the basic principles underlying the rapidly expanding field of spintronics. However, no direct demonstration of the phenomenon exists. We report a novel measurement in which a nonequilibrium spin population is created by a pointlike injection of current from a ferromagnet across a tunnel barrier into a one-dimensional spin channel and detected differentially by a pair of ferromagnetic electrodes placed symmetrically about the injection point. We demonstrate that the spin current is strictly isotropic about the injection point and, therefore, completely decoupled from the unidirectional charge current.