STM control of noninteger residual charge Q0 on the central electrode of a double-tunnel junction

In a voltage-biased mesoscopic double-tunnel junction, the Coulomb threshold V_C is an e-periodic function of Q ₀, the charge on the inner electrode. In the STM work described here, a large Au tip images 100-Å Ag particles deposited on a cleaved BSCCO crystal substrate. Stable double junctions between the tip, the imaged particle, and the substrate are identified by Coulomb staircase I(V)´s. The control of Q ₀ is demonstrated by the variation of tip-particle spacing. The parameterization of such results permits a discussion of Q ₀ variation mechanisms