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We report transport measurements through a single-molecule magnet, the Mn12 derivative [Mn12O12(O2C-C6H4-SAc)16(H2O)4], in a single-molecule transistor geometry. Thiol groups connect the molecule to gold electrodes that are fabricated by electromigration. Striking observations are regions of complete current suppression and excitations of negative differential conductance on the energy scale of the anisotropy barrier of the molecule. Transport calculations, taking into account the high-spin ground state and magnetic excitations of the molecule, reveal a blocking mechanism of the current involving nondegenerate spin multiplets.

We measure transport through gold grain quantum dots fabricated using electromigration, with magnetic impurities in the leads. A Kondo interaction is observed between dot and leads, but the presence of magnetic impurities results in a gate-dependent zero-bias conductance peak that is split due to a RKKY interaction between the spin of the dot and the static spins of the impurities. A magnetic field restores the single Kondo peak in the case of an antiferromagnetic RKKY interaction. This system provides a new platform to study Kondo and RKKY interactions in metals at the level of a single spin.

Incorporation of a third, gate electrode in the device geometry of molecular junctions necessary to identify the transport mechanism. At present, the most popular technique fabricate three-terminal molecular devices makes use of electromigration. Although it statistical process, we show that control over the gap resistance can be obtained. A detailed analysis of the current-voltage characteristics of gaps without molecules, however, shows that they reveal features that can mistakenly be attributed to molecular transport. This observation raises questions about which gaps with molecules can be disregarded which not. We show that electrical characteristics can be controlled by the rational design of the molecular bridge and that vibrational modes probed by electrical transport are potential interest as molecular fingerprints.