Combined Bloch and single-electron-tunneling oscillations in one-dimensional arrays of small tunnel junctions

It is shown that at sufficiently low temperatures, one-dimensional arrays of ultrasmall tunnel junctions (for example, semiconductor superlattices) may exhibit an unusual type of electron transfer. This process can be considered as fast ``Bloch'' oscillations with frequency fB={ε}/h (where {ε} is the electron energy change due to tunneling through one tunnel barrier), modulated with lower single-electron-tunneling frequency fS=I/e (where I is the dc electric current through the array).