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

电子是固体器件中的基本载流子，具有三种本征性质：质量、电荷和自旋。自旋是一种量子力学性质，但可以松散地想象为附加在电子上的微小的“本征”磁偶极矩。在传统的电子器件中，自旋磁矩在空间中沿随机方向定向，自旋在器件运行中不起重要作用。在新兴的“自旋电子学”领域，中心主题是使用具有明确自旋取向的“自旋极化”载流子来实现新的器件。自旋电子器件已经在最先进的硬盘驱动器和存储器中无处不在，人们正在共同努力实现基于自旋的信息处理。因此，自旋极化载流子的产生和检测在自旋电子学中是至关重要的。这类操作通常由“自旋滤光器”执行，它们优先传输具有一种特定自旋极化的载流子。根据定义，理想的自旋过滤器只传输一个特定的自旋极化，并阻止所有其他的自旋极化。这种理想的自旋过滤器在技术上是可取的，因为它们可以显著提高几乎所有自旋电子器件的性能，包括磁隧道结(MTJ)和自旋场效应晶体管(Spin-FET)。在自旋电子学中，过渡金属铁磁体传统上被用作自旋过滤器。然而，使用过渡金属铁磁体的自旋过滤远非理想。例如，通过氧化铝势垒的电子的自旋极化为~33%(镍)、42%(钴)、45%(铁)等。半金属被提出作为替代，但不幸的是，自旋过滤效率随着温度的升高而急剧恶化。因此，提高自旋过滤效率仍然是自旋电子学中的一个悬而未决的问题。在这个提议中，我们旨在通过使用非传统材料来解决这个问题，例如手性有机分子(例如脱氧核糖核酸或DNA)和石墨烯，它们由于其独特的和非传统的电子结构可以提供有效的自旋过滤。

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 importancein 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.