Magnetic Excitations of Isolated and Interconnected Complexes on a Superconductor

The magnetic complex Fe(II) porphyrin was studied on superconducting Pb(100). Low-temperature scanning tunneling microscopy was performed on isolated molecules and molecular networks prepared via Ullmann coupling. Isolated molecules adopt two distinct adsorption configurations with different magnetic excitations, namely, Yu-Shiba-Rusinov states and spin excitations. They may be understood in terms of their different magnetic anisotropies and exchange couplings with the substrate, as illustrated by the density functional theory calculations. In networks, strong intermolecular interactions lead to diverse structures with distinct magnetic and electronic properties. This work demonstrates a degree of control over the magnetic quantum states of a molecular complex on a superconductor.