Orbital-Selective Intramolecular Coexistence of Low-Energy Resonant Excitations in a Single Molecule Tunnel Junction

Abstract

We report the synthesis and purification of erbium bis-phthalocyanine (ErPc2), and the characterization of its single adsorbate on a Au(111) surface. Following a solvothermal synthesis route combined with high-performance liquid chromatography purification, we obtained high-purity ErPc2 molecules suitable for scanning tunneling microscopy/spectroscopy (STM/STS). Constant-current STM reveals intact, flat-lying molecules with well-defined topographic signatures, enabling the unambiguous identification of single adsorbates. Differential conductance measurements uncover a Kondo resonance localized in the molecular ligands, evidencing the persistence of a ligand-centered unpaired electron upon adsorption. In contrast, it shows inelastic electron tunneling features at the molecular center, a signature of discrete vibrational excitations. Density functional theory calculations reproduce the survival of the ligand spin and partial charge transfer to the substrate, whereas many-body transport modeling captures an orbital-selective electron-vibration coupling, predominantly involving nitrogen atoms and Er-N breathing modes. Our results elucidate the interplay between electronic and vibrational channels in lanthanide-based double-decker molecules on metallic substrates, providing insights into the development of molecular spintronic devices and quantum platforms using lanthanide molecules.