COULOMB OSCILLATIONS IN DOUBLE METAL TUNNEL-JUNCTIONS

The Coulomb blockade of electron tunneling through two tunnel junction s in series can be suppressed periodically by applying a gate voltage to the central island. The resulting conductance peaks (''Coulomb osci llations'') have been studied in aluminum-oxide- aluminum tunnel junct ions. For decreasing temperature the peaks narrow, in agreement with t heoretical predictions for a continuous energy spectrum of the island. We observe an increase of the conductance in the tails of the peaks f or lower resistance devices, well described by thermally enhanced inel astic electron co-tunneling.