We conduct a theoretical study of the bistable optical response of a nanoparticle heterodimer comprised of a closely spaced semiconductor quantum dot and a metal nanoparticle. The bistable nature of the response results from the interplay between the quantum dot's optical nonlinearity and its selfaction (feedback) originating from the presence of the metal nanoparticle. The feedback is governed by a complex valued coupling parameter G = G R + iG I . We calculate the bistability phase diagram within the system's parameter space: spanned by G R , G I , and , the latter being the detuning between the driving frequency and the transition frequency of the quantum dot. Additionally, switching times from the lower stable branch to the upper one (and vice versa) are calculated as a function of the intensity of the driving field. The conditions for bistability to occur can be realized, for example, for a heterodimer comprised of a closely spaced CdSe (or CdSe/ZnSe) quantum dot and a gold nanosphere. © 2013 AIP Publishing LLC. [http://dx

Explicit constructions of a (1) n affine Toda field theory breather solutions are presented. Breathers arise either from two solitons of the same species or from solitons which are anti-species of each other. In the first case, breathers carry topological charges. These topological charges lie in the tensor product representation of the fundamental representations associated with the topological charges of the constituent solitons. In the second case, breathers have zero topological charge. The breather masses are, as expected, less than the sum of the masses of the constituent solitons.

In this paper, we present experimental evidence on the change of the phonon spectrum and vibrational properties of a bulk material through phonon hybridization mechanisms. The phonon spectrum in a finite material is strongly affected by the presence of free surfaces, which is the addition of a contribution from an essentially two-dimensional crystal. The phonon spectrum of a bulk material can hence be altered by a hybridization mechanism between confined phonon modes in nanostructures introduced on the surface of a bulk material and the underlying bulk phonon modes. We measured the heat capacities of bare and surface-structured silicon substrates originating from the same silicon wafer. Then, we deduced important features of the phonon spectra of the samples investigated through a rigorous analysis of the measured heat capacity curves. The results show that the shape and size of the nanostructures made on the surface of the bulk substrate have a strong effect on the phonon spectrum of the bulk material.

Tho-photon Rabi oscillations hold potential for quantum computing and quantum information processing, because during a Rabi cycle a pair of entangled photons may be created. We theoretically investigate the onset of this phenomenon in a heterodimer comprising a semiconductor quantum dot strongly coupled to a metal nanoparticle. Two-photon Rabi oscillations in this system occur due to a coherent two-photon process involving the ground-to-biexciton transition in the quantum dot. The presence of a metal nanoparticle nearby the quantum dot results in a self-action of the quantum dot via the metal nanoparticle, because the polatization state of the latter depends on the quantum state of the former. The interparticle interaction gives rise to two principal effects: (i) -enhancement of the external field amplitude and (ii) -renormalization of the quantum dot's resonance frequencies and relaxation rates of the off-diagonal density matrix elements, both depending on the populations of the quantum dot's levels. Here, we focus on the first effect, which results in interesting new features, in particular, in an increased number of Rabi cycles per pulse as compared to an isolated quantum dot and subsequent growth of the number of entangled photon pairs per pulse. We also discuss the destructive role of radiative decay of the excitonic states on two-photon Rabi oscillations for both an isolated quantum dot and a heterodimer.

We theoretically investigate the nonlinear optical response of a heterodimer comprising a semiconductor quantum dot strongly coupled to a metal nanoparticle. The quantum dot is considered as a three-level ladder system with ground, one-exciton, and biexction states. As compared to the case of a two-level quantum dot model, adding the third (bi-exciton) state produces fascinating effects in the optical response of the hybrid system. Specifically, we demonstrate that the system may exhibit picosecond and subpicosecond self-oscillations and quasi-chaotic behaviour under single-frequency continuous wave excitation. An isolated semiconductor quantum dot does not show such features. The effects originate from competing one-exciton and bi-exciton transitions in the semiconductor quantum dot, triggered by the self-action of the quantum dot via the metal nanoparticle. The key parameter that governs the phenomena mentioned is the ratio of the self-action strength and the bi-exciton shift. The self-oscillation regime can be achieved in practice, in particular, in a heterodimer comprised of a closely spaced ZnS/ZnSe core-shell quantum dot and a spherical silver nanoparticle. The results may have applications in nanodevices for generating trains of ultrashort optical pulses.

This paper provides theoretical understanding of the interplay between the scattering of phonons by the boundaries and point-defects in SiGe thin films. It also provides a tool for the design of SiGe-based high-efficiency thermoelectric devices. The contributions of the alloy composition, grain size, and film thickness to the phonon scattering rate are described by a model for the thermal conductivity based on the single-mode relaxation time approximation. The exact Boltzmann equation including spatial dependence of phonon distribution function is solved to yield an expression for the rate at which phonons scatter by the thin film boundaries in the presence of the other phonon scattering mechanisms. The rates at which phonons scatter via normal and resistive three-phonon processes are calculated by using perturbation theories with taking into account dispersion of confined acoustic phonons in a two dimensional structure. The vibrational parameters of the model are deduced from the dispersion of confined acoustic phonons as functions of temperature and crystallographic direction. The accuracy of the model is demonstrated with reference to recent experimental investigations regarding the thermal conductivity of single-crystal and polycrystalline SiGe films. The paper describes the strength of each of the phonon scattering mechanisms in the full temperature range. Furthermore, it predicts the alloy composition and film thickness that lead to minimum thermal conductivity in a singlecrystal SiGe film, and the alloy composition and grain size that lead to minimum thermal conductivity in a polycrystalline SiGe film. VC 2015 AIP Publishing LLC.

We have examined the rational solitons in the Generalized Coupled Mode model for a deep nonlinear Bragg grating. These solitons are the degenerate forms of the ordinary solitons and appear at the transition lines in the parameter plane. A simple formulation is presented for the investigation of the bifurcations induced by detuning the carrier wave frequency. The analysis yields among others the appearance of in-gap dark and antidark rational solitons unknown in the nonlinear shallow grating. The exact expressions for the corresponding rational solitons are also derived in the process, which are characterized by rational algebraic functions. It is further demonstrated that certain effects in the soliton energy variations are to be expected when the frequency is varied across the values where the rational solitons appear.

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