Proximity coupling of magnetic and helical molecules to 2D spin-polarized electron gases – a surface transport study

邻近耦合是一种很有前途的方法来调整能带结构和调整主体材料中的输运性质。因此，禁止结构的量子性质应被修改，而带填充和电荷载流子迁移率应不受影响。这需要模板和吸附物之间的良好平衡的相互作用，这可以通过表面科学方法进行详细控制。具体而言，我们希望通过表面输运的方法来研究磁性和螺旋有机分子（功能化卟啉（Ph）、酞菁（Pc））、聚丙氨酸（PA）对二维自旋极化电子气（Bi（111）、TI）的自旋邻近效应。我们的目标是理解（定域）磁矩的屏蔽和对（离域）自旋极化电子的自旋轨道散射的影响。分子的耦合强度和自旋矩的系统变化将使我们能够理解邻近耦合的原子细节，包括自旋状态，电荷转移和对称性破缺。输运实验将系统地作为磁场（0-4 T），温度（10-300 K）和分子覆盖度（0.001-1 ML）的函数进行。输运测量的补充低温STM和STS测量。作为衬底，主要使用在Si（111）上生长的外延Bi（111）膜，但也使用拓扑绝缘体、外延Ag和膜以及石墨烯。Ph-和Pc-分子的类别允许逐渐改变局部自旋矩（不同的过渡金属核原子）以及耦合强度（例如H-、F-封端的侧基）。此外，非手性分子显示手性吸附几何形状，在没有外磁场的情况下引起时间反演对称性破缺。这一概念将详细测试使用螺旋α-L聚丙氨酸分子的异常霍尔效应的研究。我们的研究结果将为二维自旋电子器件提供新的概念。

Proximity coupling is a promising approach to tailor the band structures and to tune transport properties in a host material. Thereby, the quantum nature of the bans structure shall be modified while band filling and charge carrier mobilities should be unaffected. This demands a well-balanced interaction between the template and adsorbate, which can be controlled in detail by a surface science approach. In detail, we want to study spin-proximity effects of magnetic and helical organic molecules (functionalized porphyrins (Ph), phthalocyanines (Pc)), polyalanine (PA) towards 2D spin polarized electron gases (Bi(111), TIs) by means of surface transport. The goal is tounderstand the screening of (localized) magnetic moments and impact towards the spin orbit scattering of (delocalized) spin-polarized electrons. The systematic variation of the molecules with respect to their coupling strength and spin moments will enable us to understand atomistic details of proximity-coupling, including the spin state, charge transfer and break of symmetry. The transport experiments will be systematically performed as a function of magnetic field (0-4 T), temperature (10-300 K) and molecular coverage (0.001-1 ML). The transport measurements are complemented by low temperature STM and STS measurements. As substrate, mainly epitaxial Bi(111) films grown on Si(111), but also topological insulators, epitaxial Ag and films as well as graphene are used. The class of Ph- and Pc-molecules allow to change gradually the local spin-moment (different transition metal core atoms) as well as the coupling strengths (e.g. H-, F-terminated side groups). Moreover, the achiral molecule reveal chiral adsorption geometries, giving rise to break time reversal symmetry without external magnetic fields. This concept will be tested in detail using helical -L polyalanine molecules for anomalous Hall effect studies. Our results will provide new concepts for 2D spintronic devices.