Neoclassical Valence Bond Theory, Quantum Transport, Quantum Interference, Kondo Effect, and Electron Pumping.

Trap a single organic molecule between two electrodes and apply a bias voltage across this "molecular junction". When electrons pass through the molecule, the different electron paths can interfere destructively or constructively. Destructive interference effects in electron transport could potentially improve thermo-electrics, organic logic circuits and energy harvesting.

We have investigated destructive interference in off-resonant transport through organic molecules, and have found a set of simple rules predicting the contacting geometry, where such interference features are present.

For spin-degenerate molecular ground states the interference features become rich and can e.g. influence the Kondo enhanced conductance. We even show how some molecular junctions can produce the elusive ferromagnetic Kondo effect. The interference effects also depend on an external electrostatic gate, which in turn can control the nature (ferromagnetic or anti-ferromagnetic) of the Kondo effect in the junction.