Symmetry fingerprints of a benzene single-electron transistor: Interplay between Coulomb interaction and orbital symmetry

The interplay between Coulomb interaction and orbital symmetry produces specific transport characteristics in molecular single electron transistors (SETs) 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.

Figure 1

(Color online) The two different setups for the benzene SET considered in this paper.

Figure 2

(Color online) Stability diagram for the benzene SET connected in the para (above) and meta (below) configuration. White dot-dashed lines highlight the conductance cuts presented in Fig. 3; the white dashed line shows the region corresponding to the current trace presented in Fig. 4. The parameters used are $U=4\mid b\mid$, $V=2.4\mid b\mid$, $T=0.04\mid b\mid$, and $\Gamma ={10}^{-3}\mid b\mid$.

Figure 3

(Color online) Conductance of the benzene SET as a function of the gate voltage in the para (above) and meta (below) configurations. In the low conductance valleys, the state of the system has a definite number of particles and symmetry as indicated. Selective conductance suppression when changing from the meta to the para configuration is observed.

Figure 4

(Color online) Upper panel: Current through the benzene SET in the meta configuration calculated at bias and gate voltage conditions indicated by the dashed line of Fig. 2. A pronounced NDC is visible. Lower panels: Transition probabilities between the six-particle and each of the two seven-particle ground states for bias voltage values labeled $a-e$ in the upper panel. The transitions to a blocking state are visible in the upper (lower) part of the $e$ $\left(a\right)$ panels.