Moiré Structure and Yu-Shiba-Rusinov States of ClGa-Phthalocyanine Bilayers on Pb(100)

Chlorogallium phthalocyanine (ClGaPc) has been studied on superconducting Pb(100) using scanning tunneling microscopy and spectroscopy. The molecules assemble into well ordered bilayer islands with second-layer molecules occupying hollow sites of the first molecular layer. Topographs exhibit a moiré pattern that reflects the different adsorption sites of the first layer molecules on the Pb substrate. The lowest unoccupied molecular orbital (LUMO) resolved above the bilayer straddles the Fermi level and gives rise to Yu-Shiba-Rusinov (YSR) states. The moiré pattern breaks the degeneracy of the LUMO and affects the YSR states. Using the sharp YSR peaks for resonance enhancement, 18 vibrational excitations are resolved. Their energies appear to be independent of the moiré pattern.