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Journal of the Optical Society of America B

Optical response of a hybrid system composed of a quantum dot and a core–shell nanoparticle

Zahra Naeimi, Atefeh Mohammadzadeh, MirFaez Miri

Published Jul 31, 2019• 20 citations
Publisher

Abstract

We study a hybrid system composed of a quantum dot and a core–shell nanoparticle, subject to an external field E0 cos(ωt). We consider the self-interaction of the quantum dot due to the presence of the nanoparticle. We find that the thickness and chemical composition of both core and shell layers influence the borders between Fano, double peaks, weak transition, strong transition, and bistability regions of the phase diagram. Even weak and strong transition regions may almost disappear. The population inversion, the upper and lower limits of intensity where bistability occurs, the absorption, and other features of the system depend on the nanoparticle characteristics. This facilitates the use of the hybrid system as a miniaturized bistable device or a sensor.

DOI
10.1364/josab.36.002317

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We study a hybrid system composed of a quantum dot and a core–shell nanoparticle, subject to an external field E0 cos(ωt). We consider the self-interaction of the quantum dot due to the presence of the nanoparticle. We find that the thickness and chemical composition of both core and shell layers influence the borders between Fano, double peaks, weak transition, strong transition, and bistability regions of the phase diagram. Even weak and strong transition regions may almost disappear. The population inversion, the upper and lower limits of intensity where bistability occurs, the absorption, and other features of the system depend on the nanoparticle characteristics. This facilitates the use of the hybrid system as a miniaturized bistable device or a sensor.
We study the response of a semiconductor quantum dot-metal nanoparticle system to an external field E0 cos (ωt). The borders between Fano, double peaks, weak transition, strong transition, and bistability regions of the phase diagram move considerably as one regards the multipole effects. The exciton-induced transparency is an artifact of the dipole approximation. The absorption of the nanoparticle, the population inversion of the quantum dot, the upper and lower limits of intensity where bistability occurs, the characteristic time to reach the steady state, and other features of the hybrid system change due to the multipole effects. The phase diagrams corresponding to the fields parallel and perpendicular to the axis of system are quite distinguishable. Thus, both the intensity and the polarization of the incident field can be used to control the system. In particular, the incident polarization can be used to switch on and switch off the bistable behavior. For applications such as miniaturized bistable devices and nanosensors sensitive to variations of the dielectric constant of the surrounding medium, multipole effects must be considered.
The optical response of a hybrid structure consisting of a metal nanoparticle in the vicinity of a quantum dot under an external field is studied. The effect of the nanoparticle shape as it evolves from a sphere to a rod is investigated for various structural parameters. Significant changes are observed in the phase diagram of the optical response at the borders between Fano, exciton-induced transparency, suppression, and bistable regions. In the appropriate limits, the configuration exhibits a response where notable variations are particularly observed in suppression and bistable regions. In the presence of the nanorod, the suppression region is found as the beginning of bistability. Our calculations show that the nanorod can generate significant nonlinearities at the site of quantum dot in the bistable region, making the hybrid structure suitable for devices involving optical switching or information transfer. By considering the effect of other structural parameters, for example the configuration state, background dielectric constant, and interparticle distance, one can obtain additional control of the optical response of the system, engineering it to achieve particular objectives.
In this study, we investigate the linear optical response in a hybrid nanostructure composed of a semiconductor quantum dot and a metal shell nanoparticle. We analyze a case wherein the nanostructure interacts with an incident electromagnetic field with polarization parallel to the symmetry axis of the nanosystem. We derive nonlinear density matrix equations in the rotating wave approximation under the quasistatic response of the system, and use a series expansion method to obtain analytical functions for linear susceptibility with respect to both components of the nanostructure. The imaginary part of these expressions is related to the absorption coefficient. We investigate the way in which the modification of the core’s material affects the characteristics of the spectral resonance. For low values of the dielectric constant, the system exhibits amplified gain without population inversion and quenched absorption resonance, while for high values of the dielectric constant, we observe suppression of the gain dip and enhancement of the absorption resonance. In the first regime, the exciton lifetime is suppressed, and in the second case, its value is importantly increased, especially in the case of small interparticle distances where the semiconductor quantum dot and metal shell nanoparticle interact strongly.
We study a hybrid system composed of a chiral quantum dot and a dielectric nanoparticle subjected to an electromagnetic wave. We aim to show that the hybrid system features synergistic properties caused by interactions between its components. We solve the Bloch equation for the density matrix of the chiral quantum dot modeled as a two-level system with transition electric and magnetic dipole moments. We show that the system acts as a bianisotropic meta-atom: The electric polarization (magnetization) can be induced by the incident magnetic (electric) field. The electromagnetic and magnetoelectric polarizability dyadics of the hybrid system are influenced by the nanoparticle size and separation and the intensity and polarization of the incident wave. Due to the self-interaction of the quantum dot in the presence of the nanoparticle, the system exhibits optical activity and circular dichroism spectra of different character in Fano, double peaks, weak transition, and strong transition regions of the parameter space. Notably, in the strong transition region, the optical activity and circular dichroism spectra become discontinuous and dependent on the initial state of the system. The magnetic dipole moment induced in the dielectric nanoparticle plays a key role: Indeed, unlike the isolated chiral quantum dot, the hybrid system exhibits strong circular dichroism in a broad frequency range. The chiral quantum dot-dielectric nanoparticle meta-atom offers unique opportunities for creating low-loss all-dielectric meta-surfaces operating in the visible spectral range.
We study optical effects in a hybrid system composed of a semiconductor quantum dot and a spherical metal nanoparticle that interacts with a weak probe electromagnetic field. We use modified nonlinear density matrix equations for the description of the optical properties of the system and obtain a closed-form expression for the linear susceptibilities of the quantum dot, the metal nanoparticle, and the total system. We then investigate the dependence of the susceptibility on the interparticle distance as well as on the material parameters of the hybrid system. We find that the susceptibility of the quantum dot exhibits optical transparency for specific frequencies. In addition, we show that there is a range of frequencies of the applied field for which the susceptibility of the semiconductor quantum dot leads to gain. This suggests that in such a hybrid system quantum coherence can reverse the course of energy transfer, allowing flow of energy from the metallic nanoparticle to the quantum dot. We also explore the susceptibility of the metal nanoparticle and show that it is strongly influenced by the presence of the quantum dot.
We theoretically explore the conditions for generating optical bistability (OB) in a heterodimer comprised of a semiconductor quantum dot (SQD) and a metallic nanoshell (MNS). The MNS is made of a metallic nanosphere as a core and a dielectric material as a shell. For the specific hybrid system considered, the bistable effect appears only if the frequency of the pump field is equal to (or slightly less than) the exciton frequency for a proper shell thickness. Bistability phase diagrams, when plotted, show that the dipole-induced bistable region can be greatly broadened by changing the shell thickness of the MNS in a strong exciton-plasmon coupling regime. In particular, we demonstrate that the multipole polarization not only narrows the bistable zone but also enlarges the corresponding thresholds for a given intermediate scaled pumping intensity. On the other hand, when the SQD couples strongly with the MNS, the multipole polarization can also significantly broaden the bistable region and induce a great suppression of the FWM (four-wave mixing) signal for a fixed shell thickness. These interesting findings offer a fresh understanding of the bistability conditions in an SQD/MNS heterodimer, and may be useful in the fabrication of high-performance and low-threshold optical bistable nanodevices.