12 research outputs found
Transport spectroscopy in a time-modulated open quantum dot
We have investigated the time-modulated coherent quantum transport phenomena
in a ballistic open quantum dot. The conductance and the electron dwell
time in the dots are calculated by a time-dependent mode-matching method. Under
high-frequency modulation, the traversing electrons are found to exhibit three
types of resonant scatterings. They are intersideband scatterings: into
quasibound states in the dots, into true bound states in the dots, and into
quasibound states just beneath the subband threshold in the leads. Dip
structures or fano structures in are their signatures. Our results show
structures due to 2 intersideband processes. At the above
scattering resonances, we have estimated, according to our dwell time
calculation, the number of round-trip scatterings that the traversing electrons
undertake between the two dot openings.Comment: 8 pages, 5 figure
Differential conductance of a saddle-point constriction with a time-modulated gate-voltage
The effect of a time-modulated gate-voltage on the differential conductance
of a saddle-point constriction is studied. The constriction is modeled by a
symmetric saddle-point potential and the time-modulated gate-voltage is
represented by a potential of the form . For less than half of the transverse subband energy
level spacing, gate-voltage-assisted (suppressed) feature occurs when the
chemical potential is less (greater) than but close to the threshold
energy of a subband. As increases, is found to exhibit,
alternatively, the assisted and the suppressed feature. For larger
, these two features may overlap with one another. Dip structures
are found in the suppressed regime. Mini-steps are found in the assisted regime
only when the gate-voltage covers region far enough away from the center of the
constriction.Comment: 8 pages, 6 figure
Coherent quantum transport in the presence of a finite-range transversely polarized time-dependent field
This work investigates the quantum transport in a narrow constriction acted
upon by a finite-range transversely polarized time-dependent electric field. A
generalized scattering-matrix method is developed that has incorporated a
time-dependent mode-matching scheme. The transverse field induces coherent
inelastic scatterings that include both intersubband and intersideband
transitions. These scatterings give rise to the dc conductance a general
suppressed feature that escalates with the chemical potential. In addition,
particular suppressed features -- the dip structures -- are found in . These
features are recognized as the quasi-bound-state (QBS) features that arise from
electrons making intersubband transitions to the vicinity of a subband bottom.
For the case of larger field intensities, the QBS features that involve more
photons are more evident. These QBS features are closely associated with the
singular density of states at the subband bottoms. An experimental setup is
proposed for the observation of these features.Comment: 8 pages, 4 figure
Coherent quantum transport in narrow constrictions in the presence of a finite-range longitudinally polarized time-dependent field
We have studied the quantum transport in a narrow constriction acted upon by
a finite-range longitudinally polarized time-dependent electric field. The
electric field induces coherent inelastic scatterings which involve both
intra-subband and inter-sideband transitions. Subsequently, the dc conductance
G is found to exhibit suppressed features. These features are recognized as the
quasi-bound-state (QBS) features which are associated with electrons making
transitions to the vicinity of a subband bottom, of which the density of states
is singular. Having valley-like instead of dip-like structures, these QBS
features are different from the G characteristics for constrictions acted upon
by a finite-range time-modulated potential. In addition, the subband bottoms in
the time-dependent electric field region are shifted upward by an energy
proportional to the square of the electric field and inversely proportional to
the square of the frequency. This effective potential barrier is originated
from the square of the vector potential and it leads to the interesting
field-sensitive QBS features. An experimental set-up is proposed for the
observation of these features.Comment: 8 pages, 4 figure