Mechanical Control of Spin States in Spin-1 Molecules and the Underscreened Kondo Effect

TLDR

Electrical contact to single molecules enables probing fundamental electron‑flow processes at the nanoscale. By mechanically stretching spin‑1 cobalt complexes and altering their symmetry, the authors tuned spin states and magnetic anisotropy while measuring current, all without an external magnetic field. The spin control allowed quantitative investigation of the underscreened Kondo effect, showing that single‑molecule devices can serve as precise testbeds for correlated‑electron theories.

Abstract

The ability to make electrical contact to single molecules creates opportunities to examine fundamental processes governing electron flow on the smallest possible length scales. We report experiments in which we controllably stretched individual cobalt complexes having spin S = 1, while simultaneously measuring current flow through the molecule. The molecule's spin states and magnetic anisotropy were manipulated in the absence of a magnetic field by modification of the molecular symmetry. This control enabled quantitative studies of the underscreened Kondo effect, in which conduction electrons only partially compensate the molecular spin. Our findings demonstrate a mechanism of spin control in single-molecule devices and establish that they can serve as model systems for making precision tests of correlated-electron theories.