Doped Aromatic Thin Films with Superconducting Capabilities

多环芳烃（PAHs）是近年来出现的一类新型超导材料，其临界温度已超过30 K。有机化合物中超导性的关键因素是每个有机分子的掺杂剂原子的适当比例以及掺杂和形成的晶体结构之间的相互作用。在本研究项目中，我们旨在更深入地了解碱金属和碱土金属掺杂对物理性质的影响（即，结构，光学和电子特性）的几个多环芳烃-无论是潜在的或已经记录的超导性-在薄膜中，而不是在大多数以前的研究中使用的粉末样品。通过覆盖的厚度范围从（外延）单层膜几纳米厚，并应用选定的光谱方法，即光学差分反射光谱（DRS）和扫描隧道光谱（STS）在温度范围从300 K下降到1 K，我们将获得全面的和互补的数据来表征应用的掺杂对电子和光学性能的影响。这些测量将伴随着彻底的结构表征（MCP-LEED，ST[H]M，AFM），以获得有关掺杂对晶体结构的影响的信息，并阐明掺杂原子对掺杂单层和多层中分子的对接位点。特别是应采用扫描隧道氢显微镜（STHM），这已经成功地应用于我们的小组在分子层内的各个钾掺杂剂的精确定位。最终目标是通过STS确定相应的能隙来明确地证明超导态，并建立识别哪些PAHs是有机超导体的成功候选者的一般规则。我们的工作假设是，简并分子水平的存在可能发挥了重要作用。为了阐明这一点，我们将在我们的研究中包括不同的多环芳烃，其中一些具有简并前线轨道，其他人没有。

Polycyclic aromatic hydrocarbons (PAHs) recently emerged as a new class of superconducting materials upon doping by metal atom intercalation; with critical temperatures already higher than 30 K. Key factors for the superconductivity in the organic compounds are the appropriate ratio of dopant atoms per organic molecule as well as the interplay between the doping and the crystal structure formed. In this research project we aim at a deeper understanding of the influence of doping by alkali and earth alkali metals on the physical properties (i.e., structural, optical, and electronic properties) of several PAHs - with either potential or already documented superconductivity - in thin films, as opposed to powder samples used in most previous studies. By covering the thickness range from (epitaxial) monolayers up to films several nanometers thick and applying selected spectroscopic methods, namely optical differential reflectance spectroscopy (DRS) and scanning tunneling spectroscopy (STS) in a temperature range from 300 K down to 1 K, we shall obtain comprehensive and complementary data to characterize the influence of the applied doping on the electronic and optical properties. Those measurements will be accompanied by thorough structural characterization (MCP-LEED, ST[H]M, AFM), in order to obtain information on the influence of the doping on the crystallographic structure and to elucidate the docking sites of the doping atoms on the molecules in doped mono- and multilayers. In particular scanning tunneling hydrogen microscopy (STHM) shall be employed, which has already been successfully applied in our group for the precise location of individual potassium dopants within a molecular layer. The ultimate goal is to unequivocally demonstrate the superconducting states by determining the corresponding energy gap via STS and to establish general rules identifying which PAHs are successful candidates for organic superconductors. Our working hypothesis is that the presence of degenerate molecular levels may play a major role. To elucidate this, we will include different PAHs in our research, some of those possessing degenerate frontier orbitals, others not.