Structural Manipulation of Spin Excitations in a Molecular Junction

TL;DR

This study demonstrates how atomic-scale electrode details influence the spin excitation spectrum of a single metallocene molecule in an STM junction, revealing tunable and transition behaviors of molecular spin states.

Contribution

It provides new insights into how atomic-scale anchoring affects molecular spin states and their spectroscopic signatures in STM experiments.

Findings

Spin excitation spectrum depends on molecule-electrode anchoring.

Transition from triplet to Kondo-screened doublet observed.

Spectral line shape governed by magnetic exchange interactions.

Abstract

Single metallocene molecules act as sensitive spin detectors when decorating the probe of a scanning tunneling microscope (STM). However, the impact of the atomic-scale electrode details on the molecular spin state has remained elusive to date. Here, a nickelocene (Nc) STM junction is manipulated in an atom-wise manner showing clearly the dependence of the spin excitation spectrum on the anchoring of Nc to Cu(111), a Cu monomer and trimer. Moreover, while the spin state of the same Nc tip is a triplet with tunable spin excitation energies upon contacting the surface, it transitions to a Kondo-screened doublet on a Cu atom. Notably, the non-trivial magnetic exchange interaction of the molecular spin with the electron continuum of the substrate determines the spectral line shape of the spin excitations.