Local density of states of dc-biased superlattices with time-dependent imperfection

The single-particle Green's function for a dc-biased superlattices with single impurity potential varying harmonically with time hasbeen obtained in the framework of U(t,t') method andFloquet--Green's function. The calculation of the local density ofstates shows that new states will emerge between the resonantWannier--Stark states as a result of the intervention of time-dependent impurity potential, and the increase in electric fieldstrength of impurity will result in the growing of the number ofnew states between the gaps of neighbouring Stark ladders.