Coherent voltage oscillations in small normal tunnel junctions and the crossover to the incoherent regime

We discuss the possibility of charge oscillations in a normal tunnel junction, driven by an external current source (I
ex
), in the coherent limit. In that limit the dephasing time t
ɸ
is larger than the period t
p
≡ e/I
ex
. This behavior is modified when t
ɸ
decreases.