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Applied Sciences

Controlling the Pump-Probe Optical Response in Asymmetric Tunneling-Controlled Double Quantum Dot Molecule—Metal Nanoparticle Hybrids

Spyridon G. Kosionis, Emmanuel Paspalakis

Published Dec 9, 2021• 11 citations
Publisher

Abstract

In the present work, we investigate the modified nonlinear pump-probe optical properties due to the excitonic–plasmonic interaction of a double semiconductor quantum dot (SQD) molecule coupled to a metal nanoparticle (MNP). More specifically, we study the absorption and the dispersion spectra of a weak electromagnetic field in a hybrid structure with two counterparts, a molecule of two coupled SQDs, and a spherical MNP driven by a field of high intensity. We solve the relevant density matrix equations, calculate the first-order optical susceptibility of the probe field in the strong pumping regime, and investigate the way in which the distance between the two counterparts modifies the optical response, for a variety of values of the physical constants of the system, including the pump-field detuning, the tunnelling rate, and the energy separation gap associated with the excited states of the coupled SQDs.

DOI
10.3390/app112411714

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In the present work, we investigate the modified nonlinear pump-probe optical properties due to the excitonic–plasmonic interaction of a double semiconductor quantum dot (SQD) molecule coupled to a metal nanoparticle (MNP). More specifically, we study the absorption and the dispersion spectra of a weak electromagnetic field in a hybrid structure with two counterparts, a molecule of two coupled SQDs, and a spherical MNP driven by a field of high intensity. We solve the relevant density matrix equations, calculate the first-order optical susceptibility of the probe field in the strong pumping regime, and investigate the way in which the distance between the two counterparts modifies the optical response, for a variety of values of the physical constants of the system, including the pump-field detuning, the tunnelling rate, and the energy separation gap associated with the excited states of the coupled SQDs.
We study optical effects in a hybrid system composed of a semiconductor quantum dot (SQD) and a spherical metal nanoparticle (MNP) that interacts with a weak probe and a strong pump electromagnetic field. We use modified nonlinear density matrix equations for the description of the optical properties of the system and calculate, numerically, the first-order susceptibilities of the SQD, the MNP, and the total hybrid nanostructure of the probe field in the presence of the pump field. We investigate the dependence of the probe absorption and dispersion spectra of the SQD, the MNP, and the total nanostructure on the interparticle distance and the detuning of the pump field, and stress the influence of the MNP contribution to the total optical response. The results we find are explained according to the theory of two distinct metastates, which constitute conjugations of the SQD excitonic and the MNP plasmonic excitations. We also show that the optical response strongly depends on the actual values of the SQD material parameters.
In this study, the four-wave mixing (FWM) spectrum of a strongly pumped hybrid structure is theoretically examined. The hybrid structure consists of an asymmetric double semiconductor quantum dot (SQD) molecule and a spherical metal nanoparticle (MNP), which are coupled together via long-range Coulomb interaction. Having as a starting point the Hamiltonian of the system, in the dipole and the rotating-wave approximations, we derive a set of nonlinear density matrix equations, which are numerically solved, in the steady-state limit, and then the FWM coefficient is calculated within a range of values of the pump–probe field detuning. The spectral response of the FWM coefficient is investigated, for different values of the pump-field detuning, the electron-tunneling rate, and the energy gap between the upper states in the energy-level scheme of the double SQD molecule, while the interparticle distance between the two components of the structure is modified.
The self-Kerr nonlinear optical response of a probe field is investigated in the presence of a near-resonant pump field in coupled metal nanoparticle (MNP)–semiconductor quantum dot (SQD) nanostructures. The study of the spectra is based on the solution of the resulted density matrix equations for the case of a colloidal CdSe-based SQD–(Au)MNP molecule, as well as for an epitaxial SQD structure coupled to an Au nanoparticle. It is demonstrated that below a critical value of the interparticle distance the susceptibility of each distinct component of the structure exhibits a characteristic single-resonance spectrum, whereas above this value, the spectrum has three resonances. This phenomenon can be understood in terms of the theory of exciton–plasmon quantum metastates. In addition, the conditions under which optical transparency occurs with a concurrent positive self-phase-modulation coefficient are also identified.
The interaction of excitons with localized surface plasmons in hybrid nanostructures containing semiconductor quantum dots and metal nanoparticles, under specific conditions, may generate products with collective optical properties that have an abundance of potential applications in the area of nanotechnology. In the present study, we explore the behavior of the linear absorption and dispersion properties of the double-semiconductor quantum dot molecule in the presence of a spherical metal nanoparticle. We find that a transparency window arises in the absorption spectrum, the width of which decreases with the decrease in the electron tunnelling rate. In the low-electron-tunnelling regime, slow light is generated, an effect closely associated with tunneling-induced transparency. The enhancement of the tunneling rate induces a broadening in the transparency window, occurring due to the Autler–Townes splitting. The investigation of the impact of the distance between the quantum dot and the metal nanoparticle on the slowdown factor and the width of the transparency window shows that, by transposing the metal nanoparticle closer to the double-semiconductor quantum dot molecule, the transparency window widens.
In the present work, we theoretically/numerically study the optical second-order sideband generation in a hybrid structure consisting of a semiconductor quantum dot (QD) conjugated with DNA molecules, and coupled to a solid metallic nanoparticle (MNP) or a metallic nanoshell (MNS) with core-shell geometry. The hybrid system is driven by a strong control (pump) laser field and a weak signal (probe) field. The dynamics of the system is analyzed using the Heisenberg equation of motion in the frame of rotating wave approximation. We discuss the role of plasmon-exciton interaction in enhancing third- and fifth-order nonlinear susceptibilities through the nonlinear optical response of the system and the effects of the presence of a MNP or a MNS near the QD-DNA system on the nonlinear optical absorption spectrum is investigated. We demonstrate that the second-order sideband is generated, and the hybrid system considered here enables robust control and tunability of the second-order sidebands. It is shown that the second-order sideband spectrum (or absorption) is significantly affected by plasmonic nanoparticle size, the interparticle distance, the control field (Rabi frequency ), and the control-exciton detuning.
We investigate the optical properties appearing in a nanostructure that is composed of an asymmetric double semiconductor quantum dot (SQD) molecule and a metal nanoparticle (MNP). The profile of the total linear absorption spectrum is proportional to the SQD contribution, while the MNP contribution is important. The profile of the doublet of resonances detected on the total linear absorption spectrum creates a transparency window. The doublet is asymmetric for small SQD-MNP distances and has a narrow peak and a wide peak. The width of the transparency window is increased, either with the enhancement of the rate at which the electron tunneling effect takes place within the double SQD molecule or with the decrease of the distance that separates the SQD molecule from the center of the MNP. The steep slope detected on the linear dispersion spectrum for frequencies laying within the transparency window owes its presence to the tunneling induced transparency and leads to slow light production. The corresponding value of the slow down factor is maximized for low values of the electron tunneling rate as well as for low center-to-center distances between the components of the hybrid nanostructure.