Quantum transport in the presence of a finite-range time-modulated potential

Quantum transport in a narrow constriction and in the presence of a finite-range time-modulated potential is studied. The potential takes the form V(x,t)=V₀{θ}(x){θ}(a-x)cos({ω}t), with a the range of the potential and x the transmission direction. Intrasubband transitions for the electrons and for arbitrary {ω} are made possible by the finiteness in the potential range. Our results show that, as the chemical potential {μ} increases, the dc conductance G exhibits dip structures when {μ} is at n{}{ω} above the threshold energy of a subband. These structures in G are found in both the small a (a{~}{λ}) and the large a (a{}{λ}) regime. These dips are associated with the formation of quasi-bound-states. Our results can be reduced to the limiting case of a {δ}-profile oscillating potential when both a{}{λ} and V₀a{}1 are satisfied. The assumed form of the time-modulated potential is expected to be realized in a gate-induced potential configuration. {} 1996 The American Physical Society.