Yu-Shiba-Rusinov States of Molecules on Pb(100)

(Metal-)Phthalocyanine molecules adsorbed on a superconducting Pb(100) surface are investigated with low-temperature scanning tunneling microscopy (STM). Although the molecules are originally diamagnetic, they acquire a net magnetic moment upon assembly into supramolecules or within self-assembled islands. This effect is revealed by the observation of Yu-Shiba-Rusinov (YSR) resonances on the respective molecules.

H2-phthalocyanine (H2Pc) supramolecules are manually assembled on the surface via manipulation with the STM tip. It is shown that the lowest unoccupied molecular orbital (LUMO) of the central molecule shifts toward the Fermi level and thus becomes partially filled, which results in the net magnetic moment responsible for the YSR state. A phenomenological model is developed that explains the underlying molecular interactions. The magnetic moments are furthermore finely tuned by targeted repositioning of the inner hydrogen atoms of neighboring H2Pc molecules.

In addition, lead phthalocyanine (PbPc) molecules on Pb(100) are investigated. The influence of different adsorption geometries and neighbor molecules is studied in detail, revealing a possible influence of the electrostatic dipole moments of molecular neighbors. The sharp YSR resonances are utilized for inelastic electron tunneling spectroscopy (IETS) of molecular vibrations of PbPc. A significantly higher sensitivity is obtained compared to earlier experiments, and thus 46 separate vibrational excitations are observed. Good agreement is found in comparison with on-surface DFT calculations allowing an assignment of the observed modes. The high spectral energy resolution is used to study energy shifts of the modes caused by different influences.

Supplementary, three other molecules carrying YSR states are investigated.
Finally, the construction, test, and redesign of a home-built non-evaporable getter (NEG) pump is presented.


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