We report a measurement of the Coulomb staircase in a two-junction system where the fractional residual charge ${\mathit{Q}}_0$ on the center electrode is varied without an external electrode. We present a simple analytic equation for I(V) that depends on the parameters of the junctions, ${\mathit{C}}_{1,2}$, ${\mathit{R}}_{1,2}$, and ${\mathit{Q}}_0$, and allows us to obtain them directly from the data. Full ‘‘orthodox’’ theory simulations incorporating these parameters are in remarkable agreement with our data. Asymmetric gaplike features in the I-V curve are seen to vary with ${\mathit{Q}}_0$, and can be well understood by use of a ${\mathit{C}}_2$/${\mathit{C}}_1$-${\mathit{Q}}_0$ phase diagram.

• Received 17 June 1991

DOI:https://doi.org/10.1103/PhysRevB.44.5919