Quench of the Kondo state in a single manganese phthalocyanine molecule on gold by selective coordination

Abstract

Single-molecule spins are regarded as promising candidates for the miniaturization of magnetic storage devices at the nanoscale. The engineering of these spins can be facilitated by the Kondo effect observed in surface molecular systems, which necessitates a comprehensive understanding of the interactions between molecules and environments. In this study, we provide definitive evidence that the Kondo signature detected in a manganese phthalocyanine (MnPc) molecule adsorbed on an Au(111) surface, as indicated by previous scanning tunneling microscopy experiments, can be entirely suppressed through a chemical stimulus. This suppression is achieved by the coordination of nitric oxide (NO) and carbon monoxide (CO) as axial ligands to the molecule. Utilizing density functional theory calculations, we demonstrate that such selective coordination of CO and NO induces a considerable distortion in its molecular conformation, resulting in an increased distance between the Mn center and the substrate. This alteration diminishes the coupling with the substrate and modifies the local electronic configuration of the Mn center compared to the uncoordinated state, which accounts for the attenuation of the Kondo signature in the MnPc/Au(111) system. Specifically, when NO coordinates with the Mn center in a linear configuration, the significant hybridization between the 2π* orbital of the NO molecule and the dπ orbitals of the Mn center transforms the molecular spin state from S = 3/2 to S = 0, leading to the complete disappearance of the Kondo effect. In contrast, although the unpaired spin in the dxy orbital of the Mn center persists following CO coordination, its hybridization with the substrate near the Fermi level is insufficient due to the shape and orientation of the orbital, effectively closing the Kondo screening channel. As a result, the Kondo signature that would typically be expected from the MnPc/Au(111) system is absent after CO coordination. Our findings highlight the pivotal role of orbital symmetry in the Kondo effect, which can significantly affect hybridization with the substrate and, consequently, the Kondo screening process. The insights gained from this research provide a valuable framework for manipulating many-body quantum states in similar magnetic single-molecule adsorption systems.