Spin Filtering with Chiral Organic Molecules and Graphene: Towards Chiral Spintronics

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Electrons, the fundamental charge carriers in solid-state devices, possess three intrinsic properties: mass, charge and spin. Spin is a quantum mechanical property, but can be loosely visualized as a tiny "intrinsic" magnetic dipole moment attached to an electron. In conventional electron devices, spin magnetic moments are oriented along random directions in space and spins play no significant role in device operation. In the emerging field of "spintronics" the central theme is to use "spin-polarized" carriers with well-defined spin orientations to realize novel devices. Spintronic devices are already ubiquitous in state-of-the-art hard drives and memories and a concerted effort is underway to realize spin-based information processing. Electrical generation and detection of spin-polarized carriers are therefore of fundamental importance in spintronics. Such operations are often performed by "spin filters", which preferentially transmit carriers with one particular spin polarization. An ideal spin filter, by definition, transmits only one particular spin polarization and blocks all others. Such ideal spin filters are technologically desirable since they can significantly improve the performance of almost all spintronic devices including magnetic tunnel junctions (MTJs) and spin-field effect transistors (spin-FETs). In spintronics, transition metal ferromagnets have traditionally been used as spin filters. However, spin filtering using transition metal ferromagnets is far from ideal. For example, spin polarization of electrons tunneling through an alumina barrier is ~33% (nickel), 42% (cobalt), 45% (iron) etc. Half metals have been proposed as an alternative, but unfortunately spin filtering efficiency deteriorates drastically with increasing temperature. Thus improvement of spin filtering efficiency remains an open problem in spintronics. In this proposal we aim to address this issue by using non-traditional materials such as chiral organic molecules (e. g. Deoxyribonucleic acid or DNA) and graphene, which can offer efficient spin filtering due to their unique and unconventional electronic structures.