Current suppression in a double-island single-electron transistor for detection of degenerate charge configurations of a floating double-dot

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We have investigated a double-island single-electron transistor (DISET) coupled to a floating metal double-dot (DD). Low-temperature transport measurements were used to map out the charge configurations of both the DISET and the DD. A suppression of the current through the DISET was observed whenever the charge configurations of the DISET and the DD were energetically co-degenerate. This effect was used to distinguish between degenerate and non-degenerate charge configurations of the double-dot. We also show that this detection scheme reduces the susceptibility of the DISET to interference from random charge noise.