First-principle modelling of supramolecular spin valves: from the operational principle to the effective control

在过去的二十年里，分子电子学在实验技术和理论方面都取得了迅速的发展。现代实验技术允许分子结的制造和表征。最近的研究也集中在操纵的自旋，作为一个内在的自由度的电子，除了“外部”（空间）的自由度。超越电荷传输，这个建议是集中在一个具体的实现分子自旋电子学，其中单分子磁铁（SMM）集成到纳米结提供本地化的磁矩，并与电流相互作用。目前还没有定量模型来描述这些影响。在这个项目中，我们将建立理论基础来解释超分子自旋电子器件的机制和提高其性能，这是基于碳纳米管（CNT）修饰有几个单分子磁体。在用单个SMM装饰的CNT的第一实现中，实验观察到300%的巨大磁阻，这意味着它们作为自旋阀操作。与需要铁磁电极的已知自旋阀器件不同，这里研究的超分子自旋阀中的自旋极化器和自旋分析器的作用由单分子磁体发挥，而阀的其余部分由磁性材料（CNT和非磁性金属电极）组成。这种设置使得SMM-CNT自旋阀成为各种实际应用（即量子计算机）的合适候选者。在这个项目中，我们将使用相结合的第一性原理计算的电子结构（例如密度泛函理论（DFT）或超越）结合的非平衡绿色函数形式主义（NEGF）来阐明，如何通过纳米管的电子电流是由单分子磁体的相对取向的影响。这需要DFT和NEGF的有效和专门的组合，并建立先进的计算方法，将被集成到现有的程序包。与KIT的Wernsdörfer教授的实验组合作，我们将可能的方法来控制SMM偶极取向，例如局部门，以（1）SMM自旋非共线性的影响和（2）使用纳米碳材料而不是碳纳米管作为自旋阀通道的优势。

Over the last two decades, molecular electronics has advanced rapidly in terms of both experimental techniques and theory. Modern experimental techniques allow fabrication and characterization of molecular junctions. Recent investigations have also focused on manipulation of the spin, as an intrinsic degree of freedom of an electron, in addition to the ‘external’ (spatial) degrees of freedom. Going beyond charge transport, this proposal is focused on a specific realization of molecular spintronics, where single molecular magnets (SMMs) integrated into the nanojunction provide localized magnetic moments and interact with the current. Presently there is no quantitative model to describe these effects. In this project we are going to establish theoretical foundations to explain the mechanism and improve the performance of supramolecular spintronic devices, which are based on a carbon nanotube (CNT) decorated with several single molecular magnets. A giant magnetic resistance of 300% was experimentally observed in first realizations of CNT decorated with a single SMM, which means they operate as a spin-valve. Unlike known spin-valve devices, which require ferromagnetic electrodes, the role of spin polarizer and spin analyser in the supramolecular spin-valves investigated here is played by single-molecular magnets, and the rest of the valve consist of nonmagnetic materials (CNT and non-magnetic metal electrodes). This setup makes SMM-CNT spin valves a suitable candidate for various practical applications, i.e. quantum computers. In this project we will use combined first-principles calculations of the electronic structure (e.g. density functional theory (DFT) or beyond) combined with the nonequilibrium Green function formalism (NEGF) to elucidate, how electron current through the nanotube is affected by the relative orientation of the single-molecular magnets. This requires an effective and specialized combination of the DFT and NEGF and the establishment of advanced computational methods, which will be integrated into existing program packages. In collaboration with the experimental group of Prof. Wernsdörfer at KIT we will possible ways to control SMMs dipole orientation, e.g. the local gates, to (1) the effect of the SMMs spins noncollinearity and (2) the advantage of using nanocarbon materials other than carbon nanotube as the spin-valve channel.