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Electronic measurement and control of spin transport in silicon


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 metals1,2, semiconductors could be the most suitable for spintronics. So far, spin transport has only been measured in direct-bandgap semiconductors3,4,5,6,7,8,9 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 symmetry10,11,12. 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 μm 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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Figure 1: Illustration of the Si spin transport device.
Figure 2: Simultaneously measured current dependence on tunnel-junction emitter voltage at 85 K.
Figure 3: In-plane magnetic field dependence at 85K.
Figure 4: Spin precession and dephasing in a perpendicular magnetic field at constant emitter voltage V e = -1.8 V and 85 K.


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We acknowledge assistance during fabrication from I. Altfeder, SQUID measurements by G. Hadjipanayis and A. Gabay, and use of the wafer saw from K. Goossen. This work is supported by ONR and DARPA/MTO.

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Correspondence to Ian Appelbaum.

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Appelbaum, I., Huang, B. & Monsma, D. Electronic measurement and control of spin transport in silicon. Nature 447, 295–298 (2007).

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