Efficient Nanoscale Spin Filters

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“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.