Dynamic scattering channels of a double barrier structure

We calculate analytically the Floquet scattering matrix for a periodically driven double-barrier structure. Our approach takes into account dynamical effects which become necessarily important when electrons propagate through a system subject to a fast drive. It is convenient to represent the Floquet scattering amplitude as a sum of amplitudes corresponding to different times spent by an electron inside the structure. These amplitudes define dynamical scattering channels. Then we represent the dc current generated by the structure as a sum of two generic contributions. The first one is due to photon-assisted interference processes within the same channel and the second one is due to inter-channel interference processes. At zero temperature both contributions are present while at high temperatures and/or high driving frequencies only the former survives.