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

Abstract

Quantum transport in a narrow constriction, and in the presence of a finite-range time-modulated potential, is studied. The potential is taken the form V (x, t) = V0 θ(x)θ(a − x) cos(ωt), with a the range of the potential and x the transmission direction. As the chemical potential µ is increasing, the dc conductance G is found to exhibit dip, or peak, structures when µ is at nhω above the threshold energy of a subband. These structures in G are found in both the small a (a ≪ λF ) and the large a (a ≫ λF ) regime. The dips, which are associated with the formation of quasi-bound states, are narrower for smaller a, and for smaller V0. The locations of these dips are essentially fixed, with small shifts only in the case of large V0. Our results can be reduced to the limiting case of a delta-profile oscillating potential when both a and V0a are small. The assumed form of the time-modulated potential is expected to be realized in a gate-induced potential configuration.

Differential conductance of a saddle-point constriction with a time-modulated gate-voltage

“…Instead, the potential causes backscattering, and leads to lower dc conductances. Hence it is not unexpected that the dc conductance is found to exhibit only gate-voltage-suppressed and not gate-voltage-assisted feature [21]. As the chemical potential µ increases, the suppressed feature in the dc conductance is characterized by dip structures at which µ is mhω above the threshold energy of a subband.…”

“…The effect of such a potential on the transport properties of one dimensional systems have been investigated in many previous works [13,14,15,16,17,18,19,20,21]. However, the possible manifestation of quasibound-state (QBS) features has not been widely recognized, except for the work of Bagwell and Lake [17], who have considered a time-dependent potential that has a delta profile.…”

“…These inelastic scatterings do not conserve the longitudinal momentum along the transport direction, as long as the time-modulated fields have finite longitudinal ranges. The reason being that the finiteness in the range of the fields breaks the translational invariance [9,21]. Furthermore, the inelastic scattering processes in- duced by these time-modulated fields depend also on the polarization of the fields.…”

“…In an earlier work [21], the present authors have investigated the effect of a time-dependent gate potential acting upon the uniform-width region of a narrow constriction. For those electrons that manage to enter the narrow channel region from the two end-electrodes, they have perfect transmission, and the time-modulated potential cannot further increase the dc conductance.…”

“…These time-modulated fields can be transversely polarized [1,2,3,4,5,6,7,8,9,10], longitudinally polarized [11,12], or represented by time-modulated potentials, with no polarization [13,14,15,16,17,18,19,20,21]. The systems recently considered are mostly mesoscopic systems, such as the narrow constrictions [1,2,3,4,5,6,7,8,9,10,17,21]. For the case when a constriction is acted upon by an incident electromagnetic wave, the time-modulated field has a polarization.…”