Observation of a one-dimensional spin-orbit gap in a quantum wire

Understanding the flow of spins in magnetic layered structures has resulted in an increase in data storage density in hard drives over the past decade of more than two orders of magnitude(1). Following this remarkable success, the field of 'spintronics' or spin-based electronics(1-3) is moving beyond effects based on local spin polarization and is turning towards spin-orbit interaction (SOI) effects, which hold promise for the production, detection and manipulation of spin currents, allowing coherent transmission of information within a device(1,2). Although SOI-induced spin transport effects have been observed in two- and three-dimensional samples, these have been subtle and elusive, often detected only indirectly in electrical transport or else with more sophisticated techniques(4-9). Here we present the first observation of a predicted 'spin-orbit gap' in a one-dimensional sample, where counter-propagating spins, constituting a spin current, are accompanied by a clear signal in the easily measured linear conductance of the system(10,11). We first introduce the class of phenomena we dub 'the one-dimensional spin-orbit gap' using a simple example adapted from ref. 10, then describe our experiment in detail and finally present a more elaborate model that captures most of the features seen in our data.