Substrate stabilization of Jahn-Teller distortion in a single molecule

TL;DR

This study investigates how a substrate stabilizes Jahn-Teller distortion in a single Cu-phthalocyanine molecule, revealing charge-state-dependent structural changes and the substrate's crucial role in electronic stabilization.

Contribution

It demonstrates substrate-induced stabilization of Jahn-Teller distortion in a single molecule and provides a theoretical model explaining this effect.

Findings

Jahn-Teller distortion occurs upon formation of anionic charge states.

Substrate enhances and stabilizes the distortion.

Two electrons occupy the same localized orbital in the ground state.

Abstract

Charge-state transitions of a single Cu-phthalocyanine molecule adsorbed on an insulating layer of NaCl on Cu(111) are probed by means of alternate charging scanning tunneling microscopy. Real-space imaging of the electronic transitions reveals the Jahn-Teller distortion occurring upon formation of the first and second anionic charge states. The experimental findings are rationalized by a theoretical many-body model which highlights the crucial role played by the substrate. The latter enhances and stabilizes the intrinsic Jahn-Teller distortion of the negatively charged molecule hosting a degenerate pair of single-particle frontier orbitals. Consequently, two excess electrons are found to occupy, in the ground state, the same localized orbital, despite a larger Coulomb repulsion than the one for the competing delocalized electronic configuration. Control over the charging sequence by varying the applied bias voltage is also predicted.