Conclusions
A hybrid system consisting of an isotropic nanoparticle and a heterostructure
with a quantum well has been considered. The nanoparticle is assumed to be
polarizable in an external electric field and to have characteristic resonance
frequencies in the terahertz range. In this case, there emerge collective
oscillations of the nanoparticle polarization and plasmons in the two-dimensional
electron gas of the hybrid system.
Dispersion relations for the collective oscillation frequencies were
obtained and analyzed. Possible frequency branches were determined
and classified. Additional damping of predicted oscillations was
revealed, the origin of which is similar to that of Landau
collective damping in plasma. The electron drift results in a
reduction of the additional damping. At sufficiently high drift
velocities, owing to the energy of the electric current, there
emerges an instability in the system, and the oscillations in one of
the dispersion branches grow in time. The electric instability
increment increases, when the distance between the dipole and the
electrons diminishes and when the drift velocity increases.
The predicted effects were illustrated using the results of numerical
calculations for a shallow hydrogen-like donor in the barrier of an InAs-based
heterostructure with GaAs barriers, which were taken as an example. The
space-time dependences of concentration perturbations in the
two-dimensional electron gas in the course of collective oscillations were
analyzed. The calculated behavior was demonstrated to be substantially
different for different frequency branches, both in the absence and the presence
of drifting electrons.
The polarization oscillations of a nanoparticle were studied. It was found that
the induced dipole is characterized by a complicated dynamics at nonzero drift
velocities. In particular, in two of three branches, the dipole circulates
along elliptic trajectories depending on the electron drift parameter. It was
shown that the features in the nanoparticle polarization behavior could be
observed by measuring the emission of the hybrid system.
The practical interest to the new phenomena in hybrid systems may
consist in a capability to excite the emission by
nanoparticles by applying an electric current and the electrically
stimulated generation of THz radiation. These phenomena can also be
used for the field-controlled addressing to individual nanoparticles,
which is a key problem at the implementation of quantum calculations
\cite{Nielsen}.
The authors express their sincere
gratitude to M.V. Strikha for his attentive reading of the paper
and valuable remarks. The work was partially supported by the State
goal-oriented scientific and technical program “Nanotechnologies and nanomaterials”.
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