Nonlocal Optical Response Theory Research Articles

Multipole plasmons and their disappearance in few-nanometre silver nanoparticles.

Electron energy-loss spectroscopy can be used for detailed spatial and spectral characterization of optical excitations in metal nanoparticles. In previous electron energy-loss experiments on silver nanoparticles with radii smaller than 20 nm, only the dipolar surface plasmon resonance was assumed to play a role. Here, applying electron energy-loss spectroscopy to individual silver nanoparticles encapsulated in silicon nitride, we observe besides the usual dipole resonance an additional surface plasmon resonance corresponding to higher angular momenta for nanoparticle radii as small as 4 nm. We study the radius and electron beam impact position dependence of both resonances separately. For particles smaller than 4 nm in radius the higher-order surface plasmon mode disappears, in agreement with generalized non-local optical response theory, while the dipole resonance blueshift exceeds our theoretical predictions. Unlike in optical spectra, multipole surface plasmons are important in electron energy-loss spectra even of ultrasmall metallic nanoparticles.

Nonlocal effects on intersubband optical absorption in square quantum wells

Based on the microscopic nonlocal optical response theory, the influence from the width and depth of the potential well on the nonlocal effects and optical absorption spectra of the square quantum well is investigated in detail. The numerical results show that the radiative shift of the spectrum line, which stems from the nonlocality of optical responses, is dependent closely on the width and depth of the potential well. It is also demonstrated that the width and depth of the quantum well have important influence on the optical absorbance from the intersubband transitions. The theoretical work may be important for the growth of the nonlocal nano-materials and the potential application in optoelectronics.

Spatially nonlocal effects on optical absorption properties in coupled quantum wells with an applied electric field

Based on the microscopic nonlocal optical response theory, the intersubband optical absorption properties in AlGaAs/GaAs couple quantum wells (CQWs) are investigated for p-polarized states. The numerical results show that spatial nonlocality of optical responses can induce a radiation shift on optical absorption spectra due to nonlocal effects. The dependence of the radiation shift on the CQW structure and the applied electric field is clarified. It is also demonstrated that the maximal radiation shift and the least optical absorbance can be obtained by adopting an appropriate CQW structure and a suitable applied electric field. This work may provide some methods of designing the nanomaterials with controllable nonlocality and observing the spatial nonlocal effects in experiment.

A generalized non-local optical response theory for plasmonic nanostructures.

Metallic nanostructures exhibit a multitude of optical resonances associated with localized surface plasmon excitations. Recent observations of plasmonic phenomena at the sub-nanometre to atomic scale have stimulated the development of various sophisticated theoretical approaches for their description. Here instead we present a comparatively simple semiclassical generalized non-local optical response theory that unifies quantum pressure convection effects and induced charge diffusion kinetics, with a concomitant complex-valued generalized non-local optical response parameter. Our theory explains surprisingly well both the frequency shifts and size-dependent damping in individual metallic nanoparticles as well as the observed broadening of the crossover regime from bonding-dipole plasmons to charge-transfer plasmons in metal nanoparticle dimers, thus unravelling a classical broadening mechanism that even dominates the widely anticipated short circuiting by quantum tunnelling. We anticipate that our theory can be successfully applied in plasmonics to a wide class of conducting media, including doped semiconductors and low-dimensional materials such as graphene.

Nonlocal optical properties in InGaN/GaN strained quantum wells with a strong built-in electric field

Based on the microscopic nonlocal optical response theory, the linear and nonlinear intersubband optical absorption properties in InyGa1−yN/GaN strained single quantum wells (SQWs) with a strong built-in electric field are investigated. The numerical results show that the optical absorption spectrum has an obvious blueshift originating from the nonlocal optical responses. The dependence of the blueshift on the SQW width and the mixing fraction y is clarified. In addition, the influence of the SQW structural parameters, the incident light intensity, and the incident angle on the optical absorption properties is demonstrated. These properties are desirable for controlling the nonlocal effect and optical absorption loss in optical device application.