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AG von Oppen

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Seminars

Christoph Stampfer (ETH Zürich)
Graphene and nanotube quantum dots

We report on Coulomb blockade and Coulomb diamond measurements on an etched, tunable single-layer graphene single electron transistor (SET) and a suspended carbon nanotube. The graphene device consisting of a graphene island connected via two narrow graphene constrictions is fully tunable by three lateral graphene side gates. On the nanostructured SET Coulomb blockade resonances are observed and from Coulomb diamond measurements a charging energy of 3.5 meV is extracted. Carbon nanotubes, on the other hand, are prominent candidates to study interactions of charge carriers with (discrete) molecular vibrational modes. We report on the Franck-Condon blockade in a quantum dot formed in a suspended single-walled carbon nanotube (SWNT) device. The fourfold degeneracy of the SWNT quantum dot energy spectrum is evident in Coulomb diamond and in addition we observe excited states with energy spacings of 0.5-0.9 meV, which we attribute to longitudinal phonons in the clamped nanotube device. Finally, we observe an exponential suppression of the sequential-tunneling current at low bias.

More information: F. von Oppen (vonoppenphysik.fu-berlin.de)

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