Spintronics with graphene
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Introduction With hundreds of millions of computer hard drives sold every year, magnetism is currently, by far, the main repository of information storage. This dominance will only increase with the expected proliferation of data centers for “cloud” access over the Internet. It is the electron “spin,” the elementary nanomagnet, that carries this information. Beyond storage, spin is foreseen as the foundation for a new paradigm for information processing toward low-power-consumption nonvolatile “green” electronics. This is the aim of spintronics. However, despite intense research, a simple device such as the spin transistor proposed in 19901 has remained elusive. Whereas it was soon realized that fundamental constraints on the physics of spin transport would make this concept very difficult to achieve with conventional semiconductors such as GaAs or silicon2 (indeed, electrical injection of a spin current directly into silicon was demonstrated only recently3), a suitable material was still sought. Recently, because of its fascinating electronic properties, graphene has become the focus of expectations for producing breakthroughs in many areas of nanoelectronics.4–8 For spintronics, graphene’s obvious attraction is mainly the long spin lifetime expected from the small spin–orbit coupling of carbon atoms and the absence of nuclear spins for the main isotope.
The combination of this expected long spin lifetime with a high electron velocity, related to the linear dispersion relation of electrons in graphene, underlies the potential of graphene for spintronics. The ability to transport spin information efficiently over practical distances could further enable complex spintronic devices, such as the reconfigurable logic gate integrating both memory and logic proposed by Dery et al.,9 and eventually open the way to spin information processing. The spin diffusion distances observed in graphene are very long, in the 100-μm range, much longer than those in conventional metals and semiconductors. This is a unique advantage for several concepts of spintronic devices, particularly for complex architectures in which information is coded by pure spin currents and processed by series of logic gates acting on their spin polarization. Indeed, although a suitable platform for such devices remains to be identified, initial steps in this direction have already been taken, such as non-charge-based “beyond-CMOS” memory and logic devices highlighted in the Emerging Research Devices chapter of the International Technology Roadmap for Semiconductors (ITRS).10 Among several other spintronic devices, so-called “all-spin-logic” circuits based on the transport and processing of information coded by spin currents have been proposed.11
P. Seneor, Unité Mixte de Physique CNRS/Thales and Université Paris-Sud, France; [email protected] B. Dlubak, Unité Mixte de Physique CNRS/Thales and Université Paris-Sud, France; [email protected] M.-B. Martin, Unité Mixte de Physique CNRS/Thales and Université Paris-Sud, France; marie-blandine.
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