Light- versus electron-induced spin-state switching of complexes on insulating layers

• Applicants: Professor Manuel Gruber, Ph.D.; Professorin Dr. Carmen Herrmann; Professor Dr. Heiko Wende
• Subject Area: Experimental Condensed Matter Physics ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560970311

This project aims at investigating spin-crossover complexes in direct contact with surfaces, where the interaction of the molecules with a metal substrate is gradually tuned by inserting an insulating layer of variable thickness. We will employ temperature, light, (tunnel) electrons, and soft x-rays to trigger the spin-state switching of the complexes. Using a combination of low-temperature scanning tunneling microscopy (STM), atomic force microscopy (AFM), x-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations, we will address two core topics of the Priority Programme 2491 “Interactive Spin-State Switching”: (i) the impact of the interaction with the surrounding on the molecular switches and (ii) provide a better understanding of the switching mechanisms at the molecular level. We will achieve this by monitoring the impact of van der Waals and electrostatic interactions as well as of the electronic coupling on the geometry and electronic properties of the adsorbed complexes, as a function of the decoupling-insulating-layer thickness. In turn, we will investigate how those interactions affect the (element specific) spin-crossover properties, and more particularly on the energetic balance between the low-spin and high-spin states. We also ambition to provide an improved microscopic understanding of light- and electron-induced spin-state switching of molecules adsorbed on surfaces. Besides these direct contributions to the field, the close collaborations between the theoretical and experimental groups, with intensive trilateral exchange of information within this project together with intense exchange with partners in the Priority Programme 2491, is expected to largely contribute to the improved theoretical description of spin-crossover systems on surfaces.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2491: Interactive Spin-State Switching