Nonlocal Response Theory Research Articles

Investigation of the effect of spatial dispersion in a metal shell of a non-spherical magnetoplasmonic nanoparticle

Based on the method of discrete sources, the effect of spatial dispersion in the metal shell of a magnetoplasmonic nanoparticle on the absorption of electromagnetic energy is studied. Hybrid particle is composed of a magnetic core Fe3O4 or Fe2O3 and a golden shell. The influence of the elongation of spheroidal particles on the level of energy absorption is considered. It is shown that taking into account the spatial dispersion in the shell leads to a decrease in the absorption cross section to 30% and is accompanied by a shift of the plasmon resonance to the short-wavelength region down to 25 nm. It is found that averaging the absorption cross section over the directions of propagation of external excitation and polarizations entails a threefold decrease in the level of absorbed energy. Keywords: discrete source method, plasmon resonance, spatial dispersion, generalized nonlocal response theory.

Exciton radiative lifetime in a monoatomic carbon chain

Linear carbon-based materials such as polyyne and cumulene oligomers provide a versatile platform for nano-physics and engineering. Direct gap quasi-1D polyyne structures are promising for the observation of strong and unusual excitonic effects arising due to the two-dimensional quantum confinement. Recently, we reported on the observation of sharp exciton peaks in low temperature photoluminescence spectra of polyyne chains (Kutrovskaya S et al 2020 Nano Lett. 20 6502–9). Here, we analyze the time-resolved optical response of this system. We extend the non-local dielectric response theory to predict the exciton radiative lifetime dependence on the band-gap value and on the length of the chain. A good agreement between the experiment and the theory is achieved.

Synergetic Enhancement of Light-Matter Interaction by Nonlocality and Band Degeneracy in ZnO Thin Films.

This study aims to reveal the full potential of ZnO as an ultrafast photofunctional material. Based on nonlocal response theory to incorporate the spatially inhomogeneous quality of the samples coupled with experimental observations of linear and nonlinear optical responses, we establish the ultrafast radiative decay of excitons in ZnO thin films that reaches the speed of excitonic dephasing at room temperature in typical semiconductors at a couple tens of femtoseconds. The consistency between the observed delay-time dependence of the transient-grating signals and the theoretical prediction reveals that the ultrafast radiative decay is due to the synergetic effects of the giant light-exciton interaction volume and the radiative coupling between multicomponent excitons.

Nonlocal H-convergence

We introduce the concept of nonlocal $H$-convergence. For this we employ the theory of abstract closed complexes of operators in Hilbert spaces. We show uniqueness of the nonlocal $H$-limit as well as a corresponding compactness result. Moreover, we provide a characterisation of the introduced concept, which implies that local and nonlocal $H$-convergence coincide for multiplication operators. We provide applications to both nonlocal and nonperiodic fully time-dependent 3D Maxwell's equations on rough domains. The material law for Maxwell's equations may also rapidly oscillate between eddy current type approximations and their hyperbolic non-approximated counter parts. Applications to models in nonlocal response theory used in quantum theory and the description of meta-materials, to fourth order elliptic problems as well as to homogenisation problems on Riemannian manifolds are provided.

Microscopic theory of diffraction of light from a small hole

On the basis of the Maxwell-Lorentz local-field equations and nonlocal linear response theory, a self-consistent microscopic Green function theory of diffraction of light from a single hole in a thin and plane metallic screen is established. By subtracting the scattering of identical incident fields from screens with and without a hole, a causal effective optical aperture response tensor is introduced. An approximate expression is derived for the aperture response tensor in the limit where the screen behaves like an electric-dipole absorber and radiator. In this limit the internal electron dynamics is that of a quantum well. For a screen so thin that its bound electron motion can be described by a single quantum level, a approach for a quantum mechanical calculation of the aperture response tensor is presented. When the linear dimensions of the hole become sufficiently small the so-called aperture field, defined as the difference between the prevailing electric field with and that without a hole, becomes identical to the field from an incident-field-induced electric dipole with anisotropic linear polarizability. Our theory is formulated in such a manner that preknowledge only of (i) the incident electromagnetic field and (ii) the light-unperturbed optical electron properties (the microscopic conductivity tensor) of the screen with the geometrically given hole is needed. Since the microscopic theory allows for the presence of an (oscillating) component of the sheet current density perpendicular to the plane of the screen, a generalization of (i) the standard jump conditions of the field across the sheet and (ii) the reflection symmetries of the various fields in the plane of the screen is worked out. As our theory deviates radically from the approach of all classical diffraction theories, which are based on the macroscopic Maxwell equations and some kind of pheno-menological expression for the screen conductivity $\ensuremath{\sigma}$ (often just $\ensuremath{\sigma}\ensuremath{\rightarrow}\ensuremath{\infty})$, we give a brief review of classical diffraction theory, formulated in such a manner that a comparison to the microscopic theory is made easier. In particular, the Bethe-Bouwkamp theory of classical diffraction from a small hole in an infinitely thin and perfectly conducting $(\ensuremath{\sigma}\ensuremath{\rightarrow}\ensuremath{\infty})$ screen is our focus. We suggest that experimental frequency and angular resolved studies of the interference of the diffracted fields from quantum wells with and without holes are undertaken to obtain detailed insight into the microscopic aperture response functions, not least in the optical near-field domain.

Abnormal Absorption and Energy Flow of Electromagnetic Wave in Ultrathin Metal Films

Recently nonlocal optical responses of metal nanostructures have been investigated to better describe the abnormal optical properties of structures within a feature length of 10 nm. However, most of the investigations are based on hydrodynamical Drude model. In the present work, on the basis of the quantum nonlocal response, we study properties of s-polarization electromagnetic waves in metal films. In the studies of the dependence of absorption on frequency and thin film thickness, we find that in the case of no plasmon excitations and any scattering experienced by electrons in the system, the nonlocal response theory still gives a considerable energy absorption caused by electron–hole pair excitations. However, both the local Drude model and hydrodynamical Drude model only present zero absorption in this case. In addition, our calculation shows that the energy flow of the nonlocal-response theory displays an anomalous oscillation in the film, which is ascribed to the negative work done by electric field in some regions of the film. This is just the manifestation for the nonlocal response of current to the field.

Optical properties of CuCl microcavities with fluctuations in their refractive index profiles along the cavity structures

We report on the optical properties of the CuCl microcavities that exhibit fluctuations in their refractive index profiles along the cavity structures. The angle-resolved reflectance spectra of the CuCl microcavities with a cavity length of half-integer multiples for the ${Z}_{3}$ exciton wavelength clearly show three cavity-polariton modes and minor modes. The Rabi splitting energies observed in the cavity-polariton modes are widely controlled by changing the cavity length of the microcavity. To analyze the spectral profile and the Rabi splitting energies qualitatively, the refractive index profiles of the constituent layers in the CuCl microcavities are evaluated using spectroscopic ellipsometry, and the reflectance spectra of the CuCl microcavities with the fluctuations in the refractive index profiles of the microcavity structures are calculated using the nonlocal response theory. The calculated reflectance spectra reproduce very well the cavity-polariton modes and the minor modes, including their energies and spectral profiles, in the observed reflectance spectra, which indicates an essential role of the fluctuation effect of the refractive indices of constituent layers in controlling the Rabi splitting energies and the quality factor of the microcavity.

Microscopic formulation of nonlocal electrostatics in polar liquids embedding polarizable ions

Nonlocal electrostatic interactions associated with finite solvent size and ion polarizability are investigated within the mean-field linear response theory. To this end, we introduce a field-theoretic model of a polar liquid composed of linear multipole solvent molecules and embedding polarizable ions modeled as Drude oscillators. Unlike previous dipolar Poisson-Boltzmann formulations treating the solvent molecules as point dipoles, our model is able to qualitatively reproduce the non-local dielectric response behavior of polar liquids observed in molecular dynamics simulations and atomic force microscope experiments for water solvent at charged interfaces. The present theory explains the formation of the associated interfacial hydration layers in terms of a cooperative dipolar response mechanism driven by the reaction of the solvent molecules to their own polarization field. We also incorporate into the theory the relative multipole moments of water molecules obtained from quantum mechanical calculations and show that the multipolar contributions to the dielectric permittivity are largely dominated by the dipolar one. We find that this stems from the mutual cancellation of the first two interfacial hydration layers of opposite net charge for multipolar liquids. Within the same nonlocal dielectric response theory, we show that the induced ion polarizability reverses the interfacial ion density trends predicted by the Poisson-Boltzmann theory, resulting in a surface affinity of coions and exclusion of counterions. The results indicate that the consideration of the discrete charge composition of solvent molecules and ions is the key step towards a microscopic understanding of nonlocal electrostatic effects in polar solvents.

Exciton decay through plasmon modes in planar metal-semiconductor structures

We develop a non-local dielectric response theory to describe the temperature dependence of exciton lifetime in metal-semiconductor heterostructures. Coupling between excitons and surface plasmons results in a strongly nonmonotonous behaviour of exciton radiative decay rate versus temperature. Tuning the plasmon frequency one can control the efficiency of exciton emission of light.

Optimal design strategies for electrostatic energy storage in quantum multiwell heterostructures

We study physical principles of optimal design of a nanoscale multiwell heterostructure functioning as an electrostatic energy storage device. We performed numerical optimization of the multiwell trapping potential for electrons in the nanostructure with the goal to obtain the maximum possible static polarizability of the system. The response of the heterostructure is modeled microscopically using nonlocal linear response theory within the random phase approximation. Three main design strategies are identified which lead to the maximization of the stored energy. We found that the efficiency of each strategy crucially depends on the temperature and the broadening of electron levels. The stored energy for optimized heterostructures can exceed the nonoptimized ones by a factor of 450. These findings provide a theoretical basis for the development of new nanoscale capacitors with high energy density storage capabilities.

Second-harmonic generation from nonlocal interaction between terahertz waves and step quantum wells

Second-harmonic generation (SHG) excited by a p-polarized terahertz wave interacting with AlGaAs/GaAs step quantum wells (STQW’s) is investigated on the basis of the microscopic nonlocal response theory. The numerical results show that there are two resonant peaks in the energy reflection spectrum of the SHG, whose position and amplitude are tunable via the structural parameters of the STQW’s and the incident optical intensity. It is clarified that the spatial nonlocality of the linear and second-order nonlinear optical responses can lead to a blueshift of the second-harmonic spectra, while the third-order nonlinearity can induce a spectral redshift. Furthermore, an optimal STQW is presented, for obtaining the largest SHG signal and observing the SH spectra by experiment.

Magnetic field effect on polarization and dispersion of exciton-polaritons in planar microcavities

The non-local dielectric response theory is extended to describe oblique reflection of light from quantum wells subjected to the magnetic field. This allows us to calculate the dispersion and polarization of the exciton-polariton modes in semiconductor microcavities in the presence of a magnetic field normal to the plane of the structure. We show that due to the interplay between the exciton Zeeman splitting and TE-TM splitting of the photon modes, four polariton dispersion branches are formed with a polarization gradually changing from circular in the exciton-like part to linear in the photon-like part of each branch. Faraday rotation in quantum microcavities is shown to be strongly enhanced as compared with the rotation in quantum wells.

Ultrafast Response Induced by Interference Effects between Weakly Confined Exciton States

We report an ultrafast response of weakly confined excitons in GaAs thin films observed by a degenerate four-wave-mixing (DFWM) technique. The time-domain signals excited by broadband pulses show an oscillatory structure with a period that varies according to the pulse spectral width and an ultrafast response comparable to the pulse width; on the other hand, the exciton dephasing time is hardly changed by the excitation spectral width. This ultrafast response is much faster than the radiative lifetime expected on the basis of the nonlocal response theory. The DFWM spectra measured at various time delays clearly indicate the contribution of weakly confined excitons to the ultrafast response. Moreover, in the measurement of excitation-energy dependence, the time-domain signals excited by a controlled spectral width exhibit the variation of the oscillation period and response time. These characteristics are similar to those of the excitation spectral width dependence. From the analysis of oscillatory structu...

Optimal control of electromagnetic field using metallic nanoclusters

The dielectric properties of metallic nanoclusters in the presence of an applied electromagnetic field are investigated using the non-local linear response theory. In the quantum limit we find a nontrivial dependence of the induced field and charge distributions on the spatial separation between the clusters and on the frequency of the driving field. Using a genetic algorithm, these quantum functionalities are exploited to custom-design sub-wavelength lenses with a frequency-controlled switching capability.

Light-matter interaction in doped microcavities

We discuss theoretically the light-matter coupling in a microcavity containing a quantum well with a two-dimensional electron gas. The high density limit where the bound exciton states are absent is considered. The matrix element of an interband optical absorption demonstrates the Mahan singularity [Phys. Rev. B153, 882 (1967); 163, 612 (1967)] due to strong Coulomb effect between the electrons and a photocreated hole. We extend the nonlocal dielectric response theory to calculate the quantum well reflection and transmission coefficients as well as the microcavity transmission spectra. The new eigenmodes of the system are discussed. Their implications for the steady state and time-resolved spectroscopy experiments are analyzed.

Electromagnetic Response of Broken-Symmetry Nanoscale Clusters

A microscopic, nonlocal response theory is developed to model the interaction of electromagnetic radiation with inhomogeneous nanoscale clusters. The breakdown of classical continuum-field Mie theory is demonstrated at a critical coarse-graining threshold, below which macroscopic plasmon resonances are replaced by molecular excitations with suppressed spectral intensity.

Interaction of quantum well excitons with evanescent plane electromagnetic waves

A formalism based on non-local dielectric response theory and Green function techniqueshas been developed to describe the interaction of quantum well excitons with an evanescentoptical wave of a planar waveguide. Reflection spectra of a system in which aquantum well placed behind a dielectric interface at which light experiences totalinternal reflection have been calculated. It is shown that the spectral featurecorresponding to the exciton resonance becomes much more pronounced if the angle ofincidence is close to the critical angle of total internal reflection. The concept of ageneralized Snell law has been applied to provide simplification of the formalism.

Anomalous mode structure of a radiation–exciton coupled system beyond the long-wavelength approximation regime

We study the mode structure of a size-dependent exciton–radiation coupled system by means of nonlocal response theory. Considering excitons whose center-of-mass motion is confined in a thin film, we calculate complex eigenmodes including the radiative correction. Results show peculiar thickness dependence of the level structure and the radiative width for the region beyond the long-wavelength approximation, such as the transition from the lower to the upper polariton nature and an enhancement of the width at a particular thickness. Recently observed peculiar nonlinear responses of nondipole-type excitonic state can be explained by these results.

Semiconductor microcavities: towards polariton lasers

In this review paper we address one of the most rapidly developing new domains of semiconductor optics: light-matter coupling in semiconductor microcavities. Using the non-local dielectric response theory and transfer matrix technique, we show how two-dimensional confinement of a photonic mode coupled to an exciton resonance results in the appearance of two branches of exciton-polaritons, quasi-particles combining properties of photons and excitons. We obtain the dispersion relations of polaritons in microcavities and derive a condition for strong-weak coupling threshold. We show that being bosons, exciton-polaritons are subject to Bose-condensation which might result in emission of a coherent and monochromatic light in the strong coupling regime. A source of such coherent light is referred to as a polariton laser. We show that polariton lasers have theoretically no threshold and require essentially new basic physics as compared to conventional lasers described by Einstein theory. We give examples of model polariton laser structures expected to work at room temperature and overview the main difficulties on the way to producing these new opto-electronic devices.

Propagating mode in the photonic gap of 1D resonant Bragg reflector

Concerning “1D resonant photonic crystals”, i.e., 1D periodic arrays of resonant layers with a spacing satisfying the Bragg condition for resonant light, recent topics are summarized together with additional new findings. The central points are about (1) the recent theoretical finding of a new branch in the middle of photonic gap, (2) an approach-dependent controversy about its existence, (3) its consequence as sharp dips in reflectance spectrum and the corresponding internal field patters, indicating its propagating mode character, (4) the comparison between macroscopic and microscopic treatment of resonance effect, and (5) corrected transfer matrix method and its analytical equivalence with nonlocal response theory.