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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