(a) Simulated I-V curves and (b) corresponding dI/dV-V curves calculated using a master equation approach as described in the text. The sample bias
V
is normalized to the single electron charging energy
U
. The inset of (a) depicts the Ru-cage geometry, where the two coupled active conduction channels are drawn in red. In the case where the two coupled channels are both connected to the substrate and STM tip with similar tunneling resistances, we observe a periodic Coulomb staircase with spacing
∼
U
(blue [medium gray] curves). When one of the channels is effectively disconnected from either the STM tip or the substrate, periodic NDC emerges (green [gray] curves). (c) The charging level occupation diagram for the case where both channels are equally coupled to the tip and the substrate and conventional SET characteristics are observed. (d)–(e) The case where NDC is observed; (d) showing the level occupation of the disconnected cannel and (e) of the conducting one.