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

• Applicant: Professor Dr. Christoph Tegenkamp
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 430575550

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.

• DFG Programme: Research Grants