We present a theoretical study of two ultrasmall-capacitance normal tunnel junctions connected in series and driven by a dc voltage source, using the semiclassical junction approach. We show that the two junctions in series display a voltage offset similar to that of a single junction that is driven by a current source. We also show that two junctions in series can, for the right set of parameters, produce an I-V curve with distinct steps. A parallel array of such series units shows similar behavior. We suggest specific experimental realizations of two junctions in series and the parallel array using a scanning tunneling microscope and a granular array of small metal drops. We also compare our predictions with experiments in the literature.

• Received 10 April 1987

DOI:https://doi.org/10.1103/PhysRevB.37.98