Doped Aromatic Thin Films with Superconducting Capabilities

多环芳烃(PAHs)是近年来出现的一种新型超导材料，它的临界温度已经高于30K，决定有机化合物超导电性的关键因素是每个有机分子中掺杂原子的比例，以及掺杂与形成的晶体结构之间的相互作用。在这项研究项目中，我们旨在更深入地了解碱和土碱金属掺杂对薄膜中几种具有潜在超导电性或已有文献记载的超导多环芳烃的物理性质(即结构、光学和电子性质)的影响，而不是以往大多数研究中使用的粉末样品。通过覆盖从(外延)单分子膜到几纳米厚的薄膜的厚度范围，并在从300K到1K的温度范围内应用选定的光谱方法，即光学差示反射光谱(DRS)和扫描隧道光谱(STS)，我们将获得全面和补充的数据来表征所施加的掺杂对电子和光学性质的影响。这些测量将伴随着彻底的结构表征(MCP-LEED，ST[H]M，AFM)，以获得关于掺杂对晶体结构的影响的信息，并阐明掺杂原子在掺杂单层和多层膜中的分子对接位置。特别是，应该使用扫描隧道氢显微镜(SthM)，它已经在我们的小组中成功地应用于分子层中单个钾掺杂的精确定位。最终目标是通过STS确定相应的能隙来明确地证明超导态，并建立确定哪些多环芳烃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能级的存在可能起到主要作用。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，其中一些具有简并的前线轨道，另一些没有。

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.