Mechanical Control over Single-Molecule Spins
Understanding electrical and thermal conduction through molecular junctions is currently a topic of great interest, both theoretically using a variety of ab-initio and many-body techniques and experimentally. Novel effects arise due to the interaction between the spin, orbital and vibrational degrees of freedom of the molecule and the itinerant degrees of freedom of the conduction electrons in the leads.
The figure shows a molecular complex consisting of a Co ion in an octahedral cage of N ions connected via the surrounding ligands to the leads of a mechanical break junction. By mechanically stretching this complex, the spin anisotropy of the Co ions could be controlled and the underscreened Kondo effect could be measured.
In contrast to the usual Kondo effect, where the full spin S=1 of the Co ion is screened, the underscreened Kondo effect results in a partial screening of the spin to S=1/2 for an intermediate range of temperatures. This remnant S=1/2 couples only weakly to the leads and is easily manipulated with magnetic fields.
J. J. Parks, A. R. Champagne, T. A. Costi et al., Science 328, 170 (2010)