SPIN ELECTRONICS: Spintronics in Y-junction carbon nanotubes

该提案是对21世纪自旋电子学计划NSF 02-036的响应。该提案关注于一种独特的纳米结构系统-Y结碳纳米管的自旋相关输运和自旋电子学功能。Y结纳米管最早由PI(JMX)之一制造，它结合了碳纳米管的诱人性质(有效的一维电子传输，具有长的弹道平均自由程和极高的电流密度)，三端几何结构和Y分支点的内置异质结势垒。由另一位PI首次研究的普通直铁磁接触多壁碳纳米管中的自旋输运，产生了优异的自旋极化注入效率和约0.25微米的长自旋散射长度，使铁磁-纳米管杂化成为一种很有前途的自旋电子学平台。具有内置异质垒的Y结中的自旋输运已经很有趣，而且还没有被研究过。但所提出的器件的独特之处在于，可以将铁磁和普通金属触点同时应用于Y结的三个端子，以及使用不同的铁磁材料(具有单独可切换的磁化)用于触点到同一器件。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导的注入和引出电流与普通注入，通过第三端上的控制电压来调节自旋上下电子的传输，通过与外场切换磁化来将自旋相干电流从一个Y结臂切换到另一个Y结臂，以及更一般地产生真正的三端子自旋电子晶体管。无论这种新的纳米结构系统的潜力有多大，首先必须做大量具有挑战性的工作，从制造Y结纳米管到制造纳米级接触，再到在外部调制磁场的存在下对接触的Y结进行低温测量，以证明这些概念。这个NSF项目是为这些概念验证探索而启动的，并为通往这一新的令人兴奋的机会领域铺平了道路。

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.