Making Closed-Shell Lead-Pthalocyanine Paramagnetic on Pb(100)

Abstract

Lead phthalocyanine (PbPc), a non-planar molecule, is studied on Pb(100) using scanning tunneling spectroscopy. A rigid shift of the molecular orbitals is found between molecules with the central Pb ion pointing to (PbPc$\downarrow$) or away (PbPc$\uparrow$) from the substrate and understood from the interaction between the molecules and their image charges. Inside the superconducting energy gap, Yu-Shiba-Rusinov (YSR) resonances are observed for PbPc$\uparrow$ molecules in islands indicating the presence of a magnetic moment. Such bound states are neither present on PbPc$\downarrow$ molecules nor isolated PbPc$\uparrow$ or molecules that lost the Pb ion during deposition (H$_0$Pc). The YSR energies vary depending on the orientation and type of the molecular neighbors. We analyze the role of the out-of-plane dipole moment of PbPc.