Theoretical Studies of Chirality-Induced Spin Selectivity

利用自旋自由度来传递信息或执行逻辑运算是自旋电子学的基础。目前，大多数现有的自旋电子器件都是基于无机材料的。然而，尽管在自旋电子学中使用有机分子非常具有挑战性，但它将提供许多优势，例如可以通过化学方法调节与自旋相关的响应，以及大量合成它们的成本低廉。对于缺乏内在磁响应的分子来说，可能不会期望有很强的自旋相关性质。令人惊讶的是，几年前的实验表明，双链DNA(DsDNA)寡聚体的单层可以作为强大的自旋过滤器。一个非常有启发性的假设是，自旋选择性与目前所研究的分子(dsDNA、细菌视紫红质、螺旋寡肽、螺烯)的螺旋对称性密切相关。换句话说，似乎螺旋形状(除了可能存在的手性中心)在很大程度上要对观察到的现象负责。这些结果不仅对设计新颖的、有机的或生物启发的自旋电子器件具有深远的意义，而且还为生物相关分子中的电子转移提供了新的线索。这种新的现象被称为手性诱导自旋选择性效应。在这个方案中，我们的目标是从不同的角度从理论上探索CIS效应，目的是在它的基础上发出更多的光。参考点将是显示螺旋对称性的分子系统，这样就有可能用现实系统中的电子结构研究来补充基于模型的研究。这将有助于减少相关模型参数选择的随意性。我们期望在目前的方案中获得的结果不仅对理解几何和自旋相关性质之间的相互作用具有重要意义，而且还将作为进一步实验研究的指导和动力。

Exploiting the spin degree of freedom to transfer information or perform logic operations builds the basis of spintronics. Currently, the majority of existing spintronic devices are based on inorganic materials. However, using organic molecules in spintronics, though very challenging, would offer many advantages such as the possibility for chemically tuning the spin-dependent response as well as their inexpensive synthesis in large amounts. For molecules lacking an intrinsic magnetic response, strong spin-dependent properties may not be expected. Surprisingly, it was shown experimentally a few years ago that monolayers of double-stranded DNA (dsDNA) oligomers can act as strong spin filters. A very suggestive hypothesis has been proposed that spin selectivity is closely related to the helical symmetry of the molecules studied so far (dsDNA, bacteriorhodopsine, helical oligopeptides, helicene). In other words, it seems that the helical shape (besides the possible presence of chiral centers) is largely responsible for the observed phenomenon. These results can have profound implications not only for the design of novel, organic or bio-inspired spintronic devices but also shed new light on electron transfer in biologically relevant molecules. This novel phenomenon has been called Chirality-Induced Spin Selectivity (CISS) effect. In this proposal we are aiming at theoretically exploring the CISS effect from various perspectives with the goal of shedding additional light on its basis. The reference point will be molecular systems displaying helical symmetry so that it will be possible to complement model-based studies with electronic structure investigations in realistic systems. This will help to reduce the arbitrariness in the choice of the relevant model parameters. We expect that the results obtained in the current proposal will not only be of fundamental interest in understanding the interplay between geometry and spin-dependent properties but also serve as a guide and motivation for further experimental studies.