Efficient Nanoscale Spin Filters

“自旋电子学”是器件研究的一个活跃领域，它利用自旋的电荷载流子来存储和处理信息。自旋电子在硬盘驱动器和非易失性存储器领域已经取得了巨大的成功。在基于自旋的计算(经典的、量子的、生物的)领域正在进行重要的工作，这可能会推动设备技术超越传统的基于电荷的电子学目前面临的基本限制。在自旋电子学中，电荷载流子需要是自旋极化的--理想情况下是100%--其中所有载流子的自旋都沿着一个方向定向。 目前，自旋极化载流子是由铁磁体及其合金产生的，它们起着自旋滤光器的作用。不幸的是，这些材料提供了相对较差的自旋极化，通常约为50%或更低，这对自旋电子器件的性能产生了不利影响。例如，它导致(A)磁隧道结中的信噪比较差，以及(B)自旋场效应晶体管中的开关比较差。此外，这些材料在极纳米尺度下表现不佳，这使得缩小设备尺寸变得困难。因此，改进自旋过滤并在极小的维度上实现这一点仍然是自旋电子学的悬而未决的问题。 这个研究计划的主要目标是探索两个纳米尺度的系统，它们可能提供有效的自旋过滤：(1)锯齿形边缘的石墨烯三角形对点晶格和(2)螺旋势作用下的单壁碳纳米管。在第一种情况下，我们在石墨烯生长、纳米孔阵列制造和自旋传输测量方面的内部专业知识使我们能够探索这一领域，到目前为止，任何其他团队都没有对这一领域进行过实验研究。在第二种情况下，我们最近的结果表明，这种系统可以作为有效的自旋过滤器。然而，许多细节特征仍有待探索和了解，这将是拟议工作的重点。 这项拟议研究的主要意义在于，它将允许在极纳米尺度上进行高度的自旋过滤，这超出了当前技术的范围。拟议的系统可以导致数据存储、传感和计算的最终规模，其中原子或分子单元将作为功能元素。这将允许对经典布尔信息进行有效编码，使其处于“自旋上升”和“自旋下降”状态，而不会有因不完美极化而导致的任何“比特错误”的风险。这也将为基于自旋的量子信息处理提供高效的输入/输出接口。有效的自旋过滤将确保系统初始化和输出信息的读出/存储没有错误。因此，拟议的研究计划解决了自旋电子学中最基本的障碍之一，并可能对这一领域产生重大而广泛的影响，并将其推向最终的原子尺度极限。

“Spintronics” is an active area of device research, in which spins of charge carriers are used for information storage and processing. Spintronics has already been hugely successful in the areas of hard disk drives and non-volatile memory. Significant work is underway in the areas of spin-based computing (classical, quantum, biological), which may propel device technology beyond the fundamental limits currently faced by conventional charge based electronics. In spintronics, charge carriers are required to be spin polarized - ideally 100% - in which spins of all carriers are oriented along one direction. At present, spin polarized carriers are generated by ferromagnets and their alloys, which act as “spin filters”. Unfortunately, these materials offer relatively poor spin polarization, typically around ~50% or less, which adversely affects the performance of spintronic devices. For example, it results in (a) poor signal-to-noise ratio in magnetic tunnel junctions and (b) poor on-off ratio in spin field effect transistors. Also, these materials don't perform well at extreme nanoscale dimensions, which makes it difficult to scale down device size. Thus improvement of spin filtering and achieving this in extremely small dimensions remain as open problems in spintronics. The primary objective of this research program is to explore two nanoscale systems, which can potentially offer efficient spin filtering: (1) graphene triangular antidot lattice with zigzag edges and (2) single wall carbon nanotubes subjected to a helical potential. In the first case, our in-house expertise in graphene growth, nanopore array fabrication and spin transport measurements allow us to explore this area, which has not been investigated experimentally by any other group so far. In the second case, our recent results have shown that such systems can act as efficient spin filters. However, many detailed features remain to be explored and understood, which will be the focus of the proposed work. The main significance of the proposed research is that it will allow high degree of spin filtering in extreme nanoscale dimensions, which is beyond the scope of current technology. The proposed systems can lead to ultimate scaling in data storage, sensing and computing, where atomic or molecular units will act as functional elements. This will allow efficient encoding of classical Boolean information in “spin up” and “spin down” states, without the risk of any “bit error” due to imperfect polarization. This will also enable efficient input/output interface for spin based quantum information processing. Efficient spin filtering will ensure error-free system initialization and read-out/storage of the output information. Thus, the proposed research program addresses one of the most fundamental roadblocks in spintronics, and can have a significant and broad impact on this area and propel it toward the ultimate atomic scaling limit.