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Study of in one-dimensional conduction in nanoscale charge-density wave conductors and single molecule magnets

Final Activity Report Summary - TPLDS (Study of in one-dimensional conduction in nanoscale charge-density wave conductors and single molecule magnets)

The Marie Curie Fellowship has allowed the researcher to progress from his previous field in Charge-density waves (CDW) to the study of electrical conduction through single molecules. In the CDW work, two open questions in the electrical transport through tunnel junctions and constrictions have been answered. In the case of tunnel junctions, it is now understood why a centre peak is absent in the differential conductance versus voltage, which would be expected in the transport of a superconducting tunnel junction, a closely comparable system. This is because, unlike in a superconductor, CDW bands have an additional band corrugation which arises specifically out of its one-dimensional nature. Further, experiments on constrictions that are too large to show tunnel-like behaviour still exhibit features related to the CDW instabilities. The origin of this effect is very different from microscopic tunnelling, and is due to scattering of ungapped ballistic electrons (a feature specific to NbSe3) by the amplitude mode excitation of the CDW. A model allows the basic parameters of the CDW and the electrons to be extracted, such as the mean free path, the electron-phonon coupling and the amplitude mode energy, again highlighting the extreme one-dimensional nature of the material.

In the study of transport through single molecules, the researcher has implemented schemes to more consistently make nano-scale gaps with which to form metal electrodes. These electrodes are then used to attach single molecules and measure the electrical transport through them, typically at liquid helium temperatures. In the breaking schemes, electromigration is controlled to such a degree that the formation of the nanogap may be observed in a transmission electron microscope in real time. Further, a new 'self-breaking' effect has been observed in gold wires when only a few atoms contact the electrodes. Because this process does not involve sudden local heating of gold, the formation of spurious gold particles, which may have molecule-like transport characteristics is prevented.

Transport through single molecules of tercyclohexylidene and oligophenylenevinylene has been studied and the data has been analysed in the framework of quantum theory. In particular, the dependence of transport on temperature, vibrational degrees of freedom, and high magnetic fields is experimentally investigated and modelled.