38,252 research outputs found
Elimination of negative differential conductance in an asymmetric molecular transistor by an ac-voltage
We analyze resonant tunneling subject to a non-adiabatic time-dependent
bias-voltage through an asymmetric single molecular quantum dot with coupling
between the electronic and vibrational degrees of freedom using a {\em
Tien-Gordon-type} rate equation. Our results clearly exhibit the appearance of
photon-assisted satellites in the current-voltage characteristics and the
elimination of hot-phonon-induced negative differential conductance with
increasing ac driving amplitude for an asymmetric system. This can be ascribed
to an {\em ac-induced suppression} of unequilibrated (hot) phonons in an
asymmetric system.Comment: Accepted by Appl. Phys. Let
Finite-frequency current (shot) noise in coherent resonant tunneling through a coupled-quantum-dot interferometer
We examine the shot noise spectrum properties of coherent resonant tunneling
in coupled quantum dots in both series and parallel arrangements by means of
quantum rate equations and MacDonald's formula. Our results show that, for a
series-CQD with a relatively high dot-dot hopping ,
( denotes the dot-lead tunnel-coupling
strength), the noise spectrum exhibits a dip at the Rabi frequency, ,
in the case of noninteracting electrons, but the dip is supplanted by a peak in
the case of strong Coulomb repulsion; furthermore, it becomes a dip again for a
completely symmetric parallel-CQD by tuning enclosed magnetic-flux.Comment: 8 pages, 5 figure
Positive current noise cross-correlations in capacitively coupled double quantum dots with ferromagnetic leads
We examine cross-correlations (CCs) in the tunneling currents through two
parallel interacting quantum dots coupled to four independent ferromagnetic
electrodes. We find that when either one of the two circuits is in the parallel
configuration with sufficiently strong polarization strength, a new mechanism
of dynamical spin blockade, i.e., a spin-dependent bunching of tunneling
events, governs transport through the system together with the inter-dot
Coulomb interaction, leading to a sign-reversal of the zero-frequency current
CC in the dynamical channel blockade regime, and to enhancement of positive
current CC in the dynamical channel anti-blockade regimes, in contrast to the
corresponding results for the case of paramagnetic leads.Comment: 9 pages, 3 figure
Tunable near- to mid-infrared pump terahertz probe spectroscopy in reflection geometry
Strong-field mid-infrared pump--terahertz (THz) probe spectroscopy has been
proven as a powerful tool for light control of different orders in strongly
correlated materials. We report the construction of an ultrafast broadband
infrared pump--THz probe system in reflection geometry. A two-output optical
parametric amplifier is used for generating mid-infrared pulses with GaSe as
the nonlinear crystal. The setup is capable of pumping bulk materials at
wavelengths ranging from 1.2 m to 15 m and beyond, and detecting the
subtle, transient photoinduced changes in the reflected electric field of the
THz probe at different temperatures. As a demonstration, we present 15 m
pump--THz probe measurements of a bulk EuSbTe single crystal. A
transient change in the reflected THz electric field can be clearly resolved.
The widely tuned pumping energy could be used in mode-selective excitation
experiments and applied to many strongly correlated electron systems.Comment: 4 pages, 4 figure
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