1. Department of Electrical and Computer Engineering, University of Delaware, Newark, Delaware 19716, USA
2. Cambridge NanoTech Inc., Cambridge, Massachusetts 02139, USA

Correspondence to: Ian Appelbaum¹ Correspondence and requests for materials should be addressed to I.A. (Email: appelbaum@ee.udel.edu).

The spin lifetime and diffusion length of electrons are transport parameters that define the scale of coherence in spintronic devices and circuits. As these parameters are many orders of magnitude larger in semiconductors than in metals^{1, 2}, semiconductors could be the most suitable for spintronics. So far, spin transport has only been measured in direct-bandgap semiconductors^{3, 4, 5, 6, 7, 8, 9} or in combination with magnetic semiconductors, excluding a wide range of non-magnetic semiconductors with indirect bandgaps. Most notable in this group is silicon, Si, which (in addition to its market entrenchment in electronics) has long been predicted a superior semiconductor for spintronics with enhanced lifetime and transport length due to low spin–orbit scattering and lattice inversion symmetry^{10, 11, 12}. Despite this promise, a demonstration of coherent spin transport in Si has remained elusive, because most experiments focused on magnetoresistive devices; these methods fail because of a fundamental impedance mismatch between ferromagnetic metal and semiconductor¹³, and measurements are obscured by other magnetoelectronic effects¹⁴. Here we demonstrate conduction-band spin transport across 10 m undoped Si in a device that operates by spin-dependent ballistic hot-electron filtering through ferromagnetic thin films for both spin injection and spin detection. As it is not based on magnetoresistance, the hot-electron spin injection and spin detection avoids impedance mismatch issues and prevents interference from parasitic effects. The clean collector current shows independent magnetic and electrical control of spin precession, and thus confirms spin coherent drift in the conduction band of silicon.

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