Periodic tunnel-current oscillations in metal droplets

We have observed strong current oscillations in a metal droplet system by point-contact tunneling with a scanning tunneling microscope at 77 K. The oscillations have a periodicity equal to the single-electron charging voltage, e/C=28 mV, where C is the metal droplet capacitance. The current oscillations are large in magnitude, robust, and insensitive to tip position. A simple model of the system based on a self-biased single-electron transistor suggests the contribution of multidroplet single-electron tunneling effects. (C) 2003 American Institute of Physics.