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)=${\mathit{V}}_0$θ(x)θ(a-x)cos(ωt), 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 nħω 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 ${\mathit{V}}_0$a≪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.

• Received 26 October 1995

DOI:https://doi.org/10.1103/PhysRevB.53.4838