VARIATION OF THE COULOMB STAIRCASE IN A 2-JUNCTION SYSTEM BY FRACTIONAL ELECTRON CHARGE

We report a measurement of the Coulomb staircase in a two-junction system where the fractional residual charge Q0 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, C1,2, R1,2, and Q0, 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 Q0, and can be well understood by use of a C2/C1-Q0 phase diagram.