Coexisting Spin, Vibrational, and Orbital Excitations in Conductance Spectra

First-principles predictions of excitation energies and cross sections in inelastic tunneling spectroscopy are challenging, making it difficult to assign experimental features to specific excitations. There is, however, a need for a reliable identification of conductance features. We investigated the spin-1/2 molecule cobaltocene on superconducting Pb(110) and employ Yu-Shiba-Rusinov states combined with a superconducting tip to detect a large number of sharp spectral features. From an analysis of the peak heights at both bias voltage polarities along with model calculations and density-functional theory results we identify spin, vibrational, and orbital excitations that coexist within a single conductance spectrum. The peak height asymmetry turns out to be a useful indicator to determine the type of excitation.