Charging of Single Molecules Mediated by the Quantum Phase of Molecular Orbitals

Enriching the observable consequences of quantum phases has been a long-standing pursuit for quantum frontiers. Here, we demonstrate that the quantum phases of molecular orbitals can be manifested from the charging process of single NTCDA molecules. The self-assembled monolayer molecules form moiré patterns with the underlying Pb(111) substrate. The moiré pattern modulates the energy alignment between the molecule orbitals and the substrate Fermi level, resulting in three types of molecules. Scanning tunneling microscopy measurements indicate that all types of molecules can be gated by the tip electric field to incur charge state transitions but with different threshold fields. Intriguingly, the charge rings surrounding individual molecules exhibit intensity variations and even reversals with pertinent directional dependence. Such an observation is ascribed to the antisymmetric quantum phase of the charged molecular orbital, resulting in destructive tunneling along its highly symmetric molecular axis. This work opens up a new platform for utilizing the quantum phase of molecular orbitals in the control of charge transport in molecular junctions.