SPIN ELECTRONICS: Spintronics in Y-junction carbon nanotubes

该提案是根据21世纪自旋电子学倡议，项目征求NSF 02-036收到的。该提案的重点是在一个独特的纳米结构系统- y结碳纳米管中的自旋依赖输运和自旋电子学功能。y结纳米管，首先由一名pi （JMX）制造，结合了碳纳米管的吸引特性（有效的一维电子传输，具有长弹道平均自由路径和异常高的电流密度），三端几何结构和y分支点的内置异质结势垒。在普通的、直铁磁接触的多壁碳纳米管中的自旋输运，首先由另一位pi研究，产生了优异的自旋极化注入效率和0.25 um量级的长自旋散射长度，使铁磁-纳米管杂化物成为一个有前途的自旋电子学平台。具有内建异势垒的y结中的自旋输运已经是一个有趣且未被探索的问题。但是，该装置的独特之处在于，它可以将铁磁和普通金属触点应用于y型结的三个末端，也可以使用不同的铁磁材料（分别具有可切换的磁化强度）作为同一装置的触点。例如，这种前所未有的灵活性将使我们能够清楚地区分自旋介质注入和普通注入的电流提取，通过在第三端控制电压来调整自旋向上和自旋向下电子的传输，通过用外场切换磁化强度来将自旋相干电流从一个y结臂切换到另一个y结臂，并且更普遍地产生真正的三端自旋电子晶体管。无论这种新型纳米结构系统的潜力有多大，从y结纳米管的制造到纳米级触点的制造，再到在外部调制磁场存在下对接触的y结进行低温测量，大量具有挑战性的工作都必须首先完成，以证明这些概念。这个国家科学基金会的项目是为了这些概念验证的探索而启动的，也是为了为这个新的、令人兴奋的机会领域铺平道路。

This proposal was received in response to the Spin Electronics for the 21st Century Initiative, Program Solicitation NSF 02-036. The proposal focuses on spin dependent transport and spintronics functionality in a unique nanostructured system - Y-junction Carbon Nanotubes.The Y-junction nanotubes, first fabricated by one of the PIs (JMX)-combine the attractive properties of carbon nanotubes (effectively 1D electronic transport with long ballistic mean free paths and exceptionally high current densities)with a three-terminal geometry and a built-in heterojunction barrier at the Y-branching point. Spin transport in ordinary, straight ferromagnetically contacted multi-walled carbon nanotubes, first studied by another of the PIs, has yielded excellent spin-polarized injection efficiencies and long spin-scattering lengths on the order of 0.25 um, making ferromagnet-nanotube hybrids a promising spintronics platform. The spin transport in a Y-junction with the built-in heterobarrier is already interesting and unexplored. But what makes the proposed devices unique is the possibility applying both ferromagnetic and normal metal contacts to the three terminals of the Y-junction, as well as using different ferromagnetic materials (with separately switchable magnetizations)for contacts to the same device. This unprecedented flexibility will enable us, for example, to clearly distinguish spin-mediated injection and extraction of currents from ordinary injection, tune the transmission of spin up and spin down electrons by means of a control voltage on the third terminal, witch the spin-coherent current from one Y-junction arm to another by switching the magnetization with an external field, and more generally produce a true three-terminal spintronic transistor. However great the potential of this new nanostructured system may be, a great amount of challenging work, from fabrication of the Y-junction nanotubes to fabrication of nano-scale contacts to cryogenic measurements of the contacted Y-junctions in the presence of magnetic fields externally modulated, will have to done first to prove the concepts. This NSF project is launched for these proof-of-concept explorations, and for paving the pathway to this new and exciting field of opportunities.