Role of interference in millimeter-wave-driven dc transport in a two-dimensional electron gas

In this paper we point out that in addition to the density of states modulation, quantum interference between the multi-millimeter-wave-photon processes can cause the dc conductivity modulation observed in recent experiments. We suggest to use two radiation sources with different frequency to test the importance of quantum interference. We also present a general formalism, the linear response theory with a strong harmonic time-dependent driving field, to treat this type of transport problem.