  The interplay between Coulomb interaction and orbital symmetry produces
specific transport characteristics in molecular single electron transistors
(SET) that can be considered as the fingerprints of the contacted molecule.
Specifically we predict, for a benzene SET, selective conductance suppression
and the appearance of negative differential conductance when changing the
contacts from para to meta configuration. Both effects originate from
destructive interference in transport involving states with orbital degeneracy.

Mesoscale and Nanoscale Physics