Towards a first-principles understanding of magnetoresistance in radical molecular junctions.

对自由基分子结中磁阻的第一原理理解。

• 批准号: 420773200
• 负责人: Professorin Dr. Carmen Herrmann
• 金额: --
• 依托单位: Institut für Anorganische und Angewandte Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/420773200?language=en
• 关键词: Towards; first; principles; understanding; magnetoresistance

Controlling molecules at the individual level is a formidable task, in which tremendous progress has been made in the past years, in particular in the fields of molecular electronics and spintronics. While switching between discrete states is a particularly dramatic example of such control, gradual modification of properties such as resistance via external parameters such as magnetic fields (magnetoresistance) is intriguing because it implies that the space of accessible properties of the system can be probed broadly, and because it is essential for functionalities such as sensing. Magnetoresistance of organic radicals, contacted by metal electrodes, has the additional allure of showing unexpected behaviors, many of which are not yet understood. Elucidating the underlying physical mechanisms could provide new insight not only into the inner workings of potential functional materials, but also into fundamental aspects of molecules under nonequilibrium conditions and how they interact with metal surfaces. Our goal is precisely to gain such insight from atomistic simulations. Since several mechanisms are plausible for magnetoresistance, the most conclusive theoretical evidence would come from first-principles approaches. First-principles methods also allow for an unbiased evaluation of how chemical structure affects physical behavior, as is essential for establishing structure-property relationships once the basic mechanisms are understood.The specific goal of this project is to shed light on the mechanism of currently puzzling magnetoresistance recently observed in single-molecule TEMPO-OPE radical junctions, and to suggest new radical—electrode systems promising (a) further insight into the fundamental underlying mechanisms of magnetoresistance and interface structures, and (b) potential for spintronics applications. Our major hypothesis to be scrutinized is that radical substituents may interact with gold electrodes directly, leading to magnetic-field dependent interface modifications, which then affect transport properties. Such substituent—electrode interactions could also lead to electron transport through the radical substituent. This could lead to Kondo features, and thus could help clarify whether the lack of Kondo signatures in the experiment points to the absence of such transport pathways through the radical substituent. Therefore, we will need to describe the Kondo properties of these radicals. This includes implementing and improving computational methodology. Finally, we aim at gaining new knowledge on general structure-property relationships for organic radicals and their interactions with metal surfaces and electrodes.

在个体水平上控制分子是一项艰巨的任务，在过去的几年里，特别是在分子电子学和自旋电子学领域，已经取得了巨大的进展。虽然离散状态之间的切换是这种控制的一个特别引人注目的例子，但通过外部参数（如磁场（磁阻））逐渐修改电阻等属性是有趣的，因为它意味着可以广泛地探测系统的可访问属性的空间，并且因为它对于传感等功能至关重要。与金属电极接触的有机自由基的磁电阻具有额外的吸引力，表现出意想不到的行为，其中许多尚未被理解。阐明潜在的物理机制不仅可以为潜在功能材料的内部工作提供新的见解，还可以为非平衡条件下分子的基本方面以及它们如何与金属表面相互作用提供新的见解。我们的目标正是从原子模拟中获得这样的洞察力。由于磁电阻的多种机制都是合理的，因此最确凿的理论证据将来自第一性原理方法。第一性原理方法还允许对化学结构如何影响物理行为进行公正的评估，这对于一旦理解基本机制就建立结构-性质关系至关重要。该项目的具体目标是阐明最近在单分子TEMPO-OPE自由基结中观察到的目前令人困惑的磁阻机制，并提出新的自由基电极系统，有望（a）进一步深入了解磁电阻和界面结构的基本潜在机制，以及（B）自旋电子学应用的潜力。我们要仔细研究的主要假设是，自由基取代基可以直接与金电极相互作用，导致磁场依赖的界面修改，然后影响传输特性。这种取代基-电极相互作用也可以导致电子通过自由基取代基的传输。这可能导致近藤特征，从而有助于澄清实验中缺乏近藤特征是否表明缺乏通过自由基取代基的这种传输途径。因此，我们需要描述这些自由基的近藤性质。这包括实施和改进计算方法。最后，我们的目标是获得新的知识，一般的结构和性质的关系，有机自由基和它们与金属表面和电极的相互作用。