SHOT-NOISE SUPPRESSION IN THE SINGLE-ELECTRON TUNNELING REGIME

Electrical current fluctuations through tunnel junctions are studied w ith a scanning-tunneling microscope. For single-tunnel junctions class ical Poisson shot noise is observed, indicative for uncorrelated tunne ling of electrons. For double-barrier tunnel junctions, formed by a na noparticle between tip and surface, the shot noise is observed to be s uppressed below the Poisson value. For strongly asymmetric junctions, where a Coulomb staircase is observed in the current-voltage character istic, the shot-noise suppression is periodic in the applied voltage. This originates from correlations in the transfer of electrons imposed by single-electron charging effects.