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 Q0, the charge on the inner electrode. In our STM work, a large Au tip images 100 angstrom 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 Q0 is demonstrated by the variation of tip-particle spacing. The parameterization of such results permits a discussion of Q0 variation mechanisms.