In this paper we present a Landauer-type expression for the time-averaged dc current in a mesoscopic device illuminated by a coherent ac field, assuming phase-breaking processes to be restricted to the contacts. This expression is derived starting from the nonequilibrium Green-function formalism which rigorously accounts for the exclusion principle. However, the (1-f) factors that are often assumed do not appear in our expression. This does not affect the result if the transmission is reciprocal. But for traveling wave fields the transmission is nonreciprocal even in zero magnetic fields and the magnitude of the resulting current is affected by the presence or absence of the (1-f) factor.

• Received 2 April 1992

DOI:https://doi.org/10.1103/PhysRevB.45.13761