How To Identify Plasmons from the Optical Response of Nanostructures
Runmin Zhang, Luca Bursi, Joel D. Cox, Yao Cui, Caroline M. Krauter, Alessandro Alabastri, Alejandro Manjavacas, Arrigo Calzolari, Stefano Corni, Elisa Molinari… 展开作者
Runmin Zhang, Luca Bursi, Joel D. Cox, Yao Cui, Caroline M. Krauter, Alessandro Alabastri, Alejandro Manjavacas, Arrigo Calzolari, Stefano Corni, Elisa Molinari, Emily A. Carter, F. Javier García de Abajo, Hui Zhang, Peter Nordlander
备注：
This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Link to th original article: http://pubs.acs.org/doi/abs/10.1021/acsnano.7b03421
A promising trend in plasmonics involves shrinking the size of plasmon-supporting structures down to a few nanometers, thus enabling control over light-matter interaction at extreme-subwavelength scales. In this limit, quantum mechanical effects, such as nonlocal screening and size quantization, strongly affect the plasmonic response, rendering it substantially different from classical predictions. For very small clusters and molecules, collective plasmonic modes are hard to distinguish from other excitations such as single-electron transitions. Using rigorous quantum mechanical computational techniques for a wide variety of physical systems, we describe how an optical resonance of a nanostructure can be classified as either plasmonic or nonplasmonic. More precisely, we define a universal metric for such classification, the generalized plasmonicity index (GPI), which can be straightforwardly implemented in any computational electronic-structure method or classical electromagnetic approach to discriminate plasmons from single-particle excitations and photonic modes. Using the GPI, we investigate the plasmonicity of optical resonances in a wide range of systems including: the emergence of plasmonic behavior in small jellium spheres as the size and the number of electrons increase; atomic-scale metallic clusters as a function of the number of atoms; and nanostructured graphene as a function of size and doping down to the molecular plasmons in polycyclic aromatic hydrocarbons. Our study provides a rigorous foundation for the further development of ultrasmall nanostructures based on molecular plasmonics
Plasmons in graphene nanostructures show great promise for mid-infrared applications ranging from a few to tens of microns. However, mid-infrared plasmonic resonances in graphene nanostructures are usually weak and narrow-banded, limiting their potential in light manipulation and detection. Here we investigate the coupling among graphene plasmonic nanostructures and further show that by engineering the coupling, enhancement of light-graphene interaction strength and broadening of spectral width can be achieved simultaneously. Leveraging the concept of coupling, we demonstrate a hybrid 2-layer …
The identification of plasmons in systems below $ \sim $10 nm in size is a tremendous challenge. Any sharp distinction of the excitation character (non-plasmonic vs plasmonic) becomes blurred in this range of sizes, where quantum effects become important. Here we define a {\em plasmonicicty index} that quantifies the plasmonic character of selected optical excitations in small nanostructures, starting from first principles calculations, based on (TD)DFT. This novel approach allows us to overcome the aforementioned problems, providing a direct and quantitative classification of the plasmonic ch…
Plasmonics takes advantage of the collective response of electrons to electromagnetic waves, enabling dramatic scaling of optical devices beyond the diffraction limit. Here, we demonstrate the mid-infrared (4 to 15 microns) plasmons in deeply scaled graphene nanostructures down to 50 nm, more than 100 times smaller than the on-resonance light wavelength in free space. We reveal, for the first time, the crucial damping channels of graphene plasmons via its intrinsic optical phonons and scattering from the edges. A plasmon lifetime of 20 femto-seconds and smaller is observed, when damping throug…
Electrically tunable graphene plasmons are anticipated to enable strong light-matter interactions with resonant quantum emitters. However, plasmon resonances in graphene are typically limited to infrared frequencies, below those of optical excitations in robust quantum light sources and many biologically interesting molecules. Here we propose to utilize near fields generated by the plasmon-assisted nonlinear optical response of nanostructured graphene to resonantly couple with proximal quantum emitters operating in the near-infrared. We show that the nonlinear near-field produced by a graphene…
We develop a theory of cooperative emission of light by an ensemble of emitters, such as fluorescing molecules or semiconductor quantum dots, located near a metal nanostructure supporting surface plasmon. The primary mechanism of cooperative emission in such systems is resonant energy transfer between emitters and plasmons rather than the Dicke radiative coupling between emitters. We identify two types of plasmonic coupling between the emitters, (i) plasmon-enhanced radiative coupling and (ii) plasmon-assisted nonradiative energy transfer, the competition between them governing the structure o…
Using ab initio calculations we predict the existence of one-dimensional (1D), atomically confined plasmons at the edges of a zigzag MoS2 nanoribbon. The strongest plasmon originates from a metallic edge state localized on the sulfur dimers decorating the Mo edge of the ribbon. A detailed analysis of the dielectric function reveals that the observed deviations from the ideal 1D plasmon behavior result from single-particle transitions between the metallic edge state and the valence and conduction bands of the MoS2 sheet. The Mo and S edges of the ribbon are clearly distinguishable in calculated…
We use quantum electrodynamics and the confinement-induced nonlocal dielectric response model based on the Keldysh-Rytova electron interaction potential to study the epsilon-near-zero modes of metallic films in the transdimensional regime. New peculiar effects are revealed such as the plasmon mode degeneracy lifting and the dipole emitter coupling to the split epsilon-near-zero modes, leading to thickness-controlled spontaneous decay with up to three-orders-of-magnitude increased rates.
Classical nonlocality in conducting nanostructures has been shown to dramatically alter the linear optical response, by placing a fundamental limit on the maximum field enhancement that can be achieved. This limit directly extends to all nonlinear processes, which depend on field amplitudes. A study of third-harmonic generation in metal film-coupled nanowires reveals that for sub-nanometer vacuum gaps the nonlocality enhances the effective nonlinearity by four orders of magnitude as the field penetrates deeper inside the metal than that predicted assuming a purely local electronic response.
An ab initio theory for Fano resonances in plasmonic nanostructures and metamaterials is developed using Feshbach formalism. It reveals the role played by the electromagnetic modes and material losses in the system, and enables the engineering of Fano resonances in arbitrary geometries. A general formula for the asymmetric resonance in a non-conservative system is derived. The influence of the electromagnetic interactions on the resonance line shape is discussed and it is shown that intrinsic losses drive the resonance contrast, while its width is mostly determined by the coupling strength bet…
We investigate the excitation of electrostatic wakefields in metallic nanostructures (nanowires) due to the propagation of a short electron pulse. For that purpose, a dispersive (nonlocal) dielectric response of the system is considered, accounting for both the finiteness of the system and the quantum (Bohm) difraction of the conduction electron band, generalizing the results obtained previously in the literature [Phys. Rev. Lett. \textbf{103}, 097403 (2009)]. We discuss on the stability conditions of wakefields and show that the underling mechanism can be useful to investigate new sources of …
We theoretically explore the notion of nonreciprocal near-zone manipulation of electromagnetic fields within subwavelength plasmonic nanostructures embedded in magneto-optical materials. We derive an analytical model predicting a strong, magneto-optically induced time-reversal symmetry breaking of localized plasmonic resonances in topologically symmetric structures. Our numerical simulations of plasmon excitations reveal a considerable near-zone power flow rotation within such hybrid nanostructures, demonstrating nanoscale nonreciprocity. This can be considered as another mechanism for tuning …
Localized plasmons in metallic nanostructures have been widely used to enhance nonlinear optical effects due to their ability to concentrate and enhance light down to extreme-subwavelength scales. As alternatives to noble metal nanoparticles, graphene nanostructures can host long-lived plasmons that efficiently couple to light and are actively tunable via electrical doping. Here we show that doped graphene nanoislands present unique opportunities for enhancing nonlinear optical wave-mixing processes between two externally applied optical fields at the nanoscale. These small islands can support…
Plasmonic metal nanostructures are an integral part of nanophotonic device applications owing to their ability to generate strong localized electromagnetic fields when illuminated from the far-field. These nanostructures can be prepared in the laboratory with precise shape and size by various chemical and physical synthesis techniques as demonstrated in recent years. Typically, the size of these structures is in the range of few nm to a few hundred nm, i.e., much below the wavelength of light of observation or excitation. The focus of this chapter is to exploit the ultrafast response of metal …
In this paper we discuss the field enhancement due to surface plasmons resonances of metallic nanostructures, in particular nano spheres on top of a metal, and find maximum field enhancement of the order of 10^2, intensities enhancement of the order of 10^4. Naturally these fields can produce temporal fields of the order of 0.5V/Å that yield field emission of electrons. Although the fields enhancements we calculated are factor of 10 smaller than those reported in recent experiments, our results explain very well the experimental data. Very large atomic fields destabilize the system completely …
We develop a quantum-mechanical theory for Landau damping of surface plasmons in metal nanostructures larger that the characteristic length for nonlocal effects. We show that the electron surface scattering, which facilitates plasmon decay in small nanostructures, can be incorporated into the metal dielectric function on par with phonon and impurity scattering. The derived surface scattering rate is determined by the plasmon local field polarization relative to the metal-dielectric interface and is highly sensitive to the system geometry. We illustrate our model by providing analytical results…
When the sizes of photonic nanoparticles are much smaller than the excitation wavelength, their optical response can be efficiently described with a series of polarizability tensors. Here, we propose a universal method to extract the different components of the response tensors associated with small plasmonic or dielectric particles. We demonstrate that the optical response can be faithfully approximated, as long as the effective dipole is not induced by retardation effects, hence do not depend on the phase of the illumination. We show that the conventional approximation breaks down for a phas…
Hybrid plasmonic devices involve a nanostructured metal supporting localized surface plasmons to amplify light-matter interaction, and a non-plasmonic material to functionalize charge excitations. Application-relevant epitaxial heterostructures, however, give rise to ballistic ultrafast dynamics that challenge the conventional semiclassical understanding of unidirectional nanometal-to-substrate energy transfer. We study epitaxial Au nanoislands on WSe$_2$ with time- and angle-resolved photoemission spectroscopy and femtosecond electron diffraction: this combination of techniques resolves mater…
Nonlinear plasmonic effects in perspective 2D materials containing low-dimensional quantum emitters can be a basis of a novel technological platform for the fabrication of fast all-plasmonic triggers, transistors, and sensors. This article considers the conditions for achieving a strong plasmon-exciton coupling in the system with quantum nanowire (NW) placed in proximity to the nanostructured graphene sheets. In the condition of strong coupling, nonlinear interaction between two surface plasmon-polariton (SPP) modes propagating along the graphene waveguide integrated with a stub nanoresonator …
The rate of spontaneous emission is known to depend on the environment of a light source, and the enhancement of one-photon emission in a resonant cavity is known as the Purcell effect. Here we develop a theory of spontaneous two-photon emission for a general electromagnetic environment including inhomogeneous dispersive and absorptive media. This theory is used to evaluate the two-photon Purcell enhancement in the vicinity of metallic nanoparticles and it is demonstrated that the surface plasmon resonances supported by these particles can enhance the emission rate by more than two orders of m…
We develop a unified theory of plasmon-assisted resonance energy transfer (RET) between molecules near a metal nanostructure that maintains energy balance between transfer, dissipation, and radiation. We show that in a wide range of parameters, including in the near field, RET is dominated by plasmon-enhanced radiative transfer (PERT) rather than by a nonradiative transfer mechanism. Our numerical calculations performed for molecules near the Ag nanoparticle indicate that RET magnitude is highly sensitive to molecules' positions.
We present a quantum-mechanical model for surface-assisted carrier excitation by optical fields in plasmonic nanostructures of arbitrary shape. We derive an explicit expression, in terms of local fields inside the metal structure, for surface absorbed power and surface scattering rate that determine the enhancement of carrier excitation efficiency near the metal-dielectric interface. We show that surface scattering is highly sensitive to the local field polarization, and can be incorporated into metal dielectric function along with phonon and impurity scattering. We also show that the obtained…
We theoretically examine the role of Kerr nonlinearities for graphene plasmonics in nanostructures, specifically in nanoribbons. The nonlinear Kerr interaction is included semiclassically in the intraband approximation. The resulting electromagnetic problem is solved numerically by self-consistent iteration with linear steps using a real-space discretization. We derive a simple approximation for the resonance shifts in general graphene nanostructures, and obtain excellent agreement with numerics for moderately high field strengths. Near plasmonic resonances the nonlinearities are strongly enha…
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A new approach of using distributed transmission line analogy for solving transport equations for ballistic nanostructures is applied for solving the three dimensional problem of the electron transport in gated ballistic nanostructures with periodically changing width. The structures with the varying width allow for modulation of the electron drift velocity while keeping the plasma velocity constant. We predict that in such structures biased by a constant current, a periodic modulation of the electron drift velocity due the varying width results in the instability of the plasma waves if the el…
The use of magneto-optical techniques to tune the plasmonic response of nanostructures is a hot topic in active plasmonics, with fascinating implications for several plasmon-based applications and devices. For this emerging field, called magnetoplasmonics, plasmonic nanomaterials with strong optical response to magnetic field are desired, which is generally challenging to achieve with pure noble metals. To overcome this issue, several efforts have been carried out to design and tailor the magneto-optical response of metal nanostructures, mainly by combining plasmonic and magnetic materials in …
The material and exact shape of a nanostructure determine its optical response, which is especially strong for plasmonic metals. Unfortunately, only a very few plasmonic metals are available, which limits the spectral range where these strong optical effects can be utilized. Alloying different plasmonic metals can overcome this limitation, at the expense of using a high temperature alloying process, which adversely destroys the nanostructure shape. Here, we develop a low temperature alloying process at only 300°C and fabricate Au-Ag nanostructures with a broad diversity of shapes, aspect ratio…
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A significant interest in combining plasmonics and magnetism at the nanoscale gains momentum in both photonics and magnetism sectors that are concerned with the resonant enhancement of light-magnetic-matter interaction in nanostructures. These efforts result in a considerable amount of literature, which is difficult to collect and digest in limited time. Furthermore, there is insufficient exchange of results between the two research sectors. Consequently, the goal of this review paper is to bridge this gap by presenting an overview of recent progress in the field of magneto-plasmonics from two…
Heat-transport mechanism mediated by near-field interactions in plasmonic nanostructures networks is shown to be analogous to a generalized random-walk process. Existence of superdiffusive regimes is demonstrated both in linear ordered chains and in three dimensional random networks by analyzing the asymptotic behavior of the corresponding probability distribution function. We show that the spread of heat in these networks is described by a type of Lévy flight. The presence of such anomalous heat transport regimes in plasmonic networks opens the way to the design of a new generation of composi…
Plasmonic resonance of a metallic nanostructure results from coherent motion of its conduction electrons driven by incident light. At the resonance, the induced dipole in the nanostructure is proportional to the number of the conduction electrons, hence $10^{7}$ times larger than that in an atom. The interaction energy between the induced dipole and fluctuating virtual field of the incident light can reach a few tenths of an eV. Therefore, the classical electromagnetism dominating the field becomes inadequate. We argue that quantum electrodynamics (QED) should be used instead as the fundamenta…
We report on reflection spectra of caesium atoms in close vicinity of a nanostructured metallic meta-surface. We show that the hyperfine sub-Doppler spectrum of the $6S_{1/2} - 6P_{3/2}$ resonance transition at 852 nm is strongly affected by the coupling to the plasmonic resonance of the nanostructure. Fine tuning of dispersion and positions of the atomic lines in the near-field of plasmonic metamaterials could have uses and implications for the atom-based metrology, sensing and the development of atom-on-a-chip devices.
Metal nanostructures can be used to harvest and guide the emission of single photon emitters on-chip via surface plasmon polaritons. In order to develop and characterize photonic devices based on emitter-plasmon hybrid structures a deterministic and scalable fabrication method for such structures is desirable. Here we demonstrate deterministic and scalable top-down fabrication of metal wires onto preselected nitrogen vacancy centers in nanodiamonds using clean room nano-fabrication methods. We observe a life-time reduction of the emitter emission that is consistent with earlier proof-of-princi…
Graphene is a unique material to study fundamental limits of plasmonics. Apart from the ultimate single-layer thickness, its carrier concentration can be tuned by chemical doping or applying an electric field. In this manner the electrodynamic properties of graphene can be varied from highly conductive to dielectric. Graphene supports strongly confined, propagating surface plasmon-polaritons (SPPs) in a broad spectral range from terahertz to mid-infrared frequencies. It also possesses a strong magneto-optical response and thus provides complimentary architectures to conventional magneto-plasmo…
We demonstrate the direct photothermal probing and mapping of single plasmonic nanostructures via the temperature induced detuning of nanomechanical string resonators. Single Au nanoslits are illuminated with a low-power polarized focused laser beam (λ = 633 nm). Polarization dependent heat generation in gold nanoslits is then imaged with high sensitivity. A sensitivity of -4.1 ppm/nW with respect to the illuminated light (beam diameter 5.0pm0.8 μm) is determined for a single nanoslit (1 μm long and 53 nm wide), which equals to a total light absorption of 16%. This results in a heating of 0.5 …
Usually, the liner waveguides with single quantum emitters are utilized as routers to construct the quantum network in quantum information processings. Here, we investigate the influence of the nonlinear dispersion on quantum routing of single surface plasmons, between two metal nanowires with a pair of quantum dots. By using a full quantum theory in real space, we obtain the routing probabilities of a single surface plasmon into the four outports of two plasmonic waveguides scattered by a pair of quantum dots. It is shown that, by properly designing the inter-dot distance and the dot-plasmon …
Metal nanowires and nanoparticles that facilitate surface plasmons are of contemporary interest in nanophotonics, thermoplasmonics and optoelectronics. They facilitate not only subwavelength light propagation and localization capabilities, but also provide an excellent platform for opto-thermal effects confined to volumes down to the nanoscale. This brief review article aims to provide an overview of a specific nanophotonic geometry: a plasmonic nanowire coupled to a zero-dimensional nanostructure. We discuss the methods to prepare such nano-architectures and review some interesting nanophoton…
We demonstrate propagation of plasmons in single crystalline silver nanostructures fabricated using a combination of a bottom-up and a top-down approach. Silver nanoplates of thickness around 65 nm and a surface area of about 100 μm^2 are made using a wet chemical method. Silver nanotips and nanowires are then sculptured by focused ion beam milling. The plasmons are excited by using the fluorescence from the redeposited silver clusters during the milling process. Propagation of plasmons in the nanowires is observed in the visible spectral region. We also observe a cavity effect by measuring th…
Using the Green's dyad technique based on cuboidal meshing, we compute the electromagnetic field scattered by metal nanorods with high aspect ratio. We investigate the effect of the meshing shape on the numerical simulations. We observe that discretizing the object with cells with aspect ratios similar to the object's aspect ratio improves the computations, without degrading the convergency. We also compare our numerical simulations to finite element method and discuss further possible improvements.
The knowledge of the carrier dynamics in nanostructures is of fundamental importance for the development of (opto)electronic devices. This is true for semiconducting nanostructures as well as for plasmonic nanoparticles (NPs). Indeed, improvement of photocatalytic efficiencies by combining semiconductor and plasmonic nanostructures is one of the reasons why their ultrafast dynamics are intensively studied. In this work, we will review our activity on ultrafast spectroscopy in nanostructures carried out in the recently established EuroFEL Support Laboratory. We have investigated the dynamical p…
The discovery of many fascinating new phenomena associated with the surface plasmon polariton (SPP) has triggered the rapid development of nanophotonics and nanoelectronics. We report here the experimental observation of a fundamentally new physical process, nonlinear electron scattering, stimulated by the SPP excitation of Ag nanostructures on graphite surface in scanning probe electron energy loss spectroscopy. The observed intensity of SPP energy loss peak normalized to the elastic scattering intensity shows clearly a quadratic dependence on the external electric field strength generated by…
The Fano and Rabi models represent remarkably common effects in optics. Here we study the coherent time dynamics of plasmonic systems exhibiting Fano and Rabi resonances. We demonstrate that these systems show fundamentally different dynamics. A system with a Fano resonance displays at most one temporal beat under pulsed excitation, whereas a system in the Rabi regime may have any number of beats. Remarkably, the Fano-like systems show time dynamics with very characteristic coherent tails despite the strong decoherence that is intrinsic for such systems. The coherent Fano and Rabi dynamics tha…
Tomonaga-Luttinger (T-L) theory predicts collective plasmon resonances in 1-D nanostructure conductors of finite length, that vary roughly in inverse proportion to the length of the structure. In-depth quantitative understanding of such resonances which have not been clearly identified in experiments so far, would be invaluable for future generations of nano-photonic and nano-electronic devices that employ 1-D conductors. Here we provide evidence of the plasmon resonances in a number of representative 1-D finite carbon-based nanostructures using first-principle computational electronic spectro…
We explore the collective electromagnetic response in atomic clusters of various sizes and geometries. Our aim is to understand, and hence to control, their dielectric response, based on a fully quantum-mechanical description which captures accurately their relevant collective modes. The electronic energy levels and wave functions, calculated within the tight-binding model, are used to determine the non-local dielectric response function. It is found that the system shape, the electron filling and the driving frequency of the external electric field strongly control the resonance properties of…
Aluminum, as a metallic material for plasmonics, is of great interest because it extends the applications of surface plasmon resonance into the ultraviolet (UV) region and excels noble metals in the natural abundance, cost and compatibility with modern semiconductor fabrication process. Here, we present UV to near-infrared (NIR) plasmonic resonance of single-crystalline aluminum nanoslits and nanoholes. The high-definition nanostructures are fabricated with focused ion-beam (FIB) milling into an ultrasmooth single-crystalline aluminum film grown on a semiconducting GaAs substrate with molecula…
The ability to harness light-matter interactions at the few-photon level plays a pivotal role in quantum technologies. Single photons - the most elementary states of light - can be generated on-demand in atomic and solid state emitters. Two-photon states are also key quantum assets, but achieving them in individual emitters is challenging because their generation rate is much slower than competing one-photon processes. We demonstrate that atomically thin plasmonic nanostructures can harness two-photon spontaneous emission, resulting in giant far-field two-photon production, a wealth of resonan…
Plasmonic hot carrier devices extract excited carriers from metal nanostructures before equilibration, and have the potential to surpass semiconductor light absorbers. However their efficiencies have so far remained well below theoretical limits, which necessitates quantitative prediction of carrier transport and energy loss in plasmonic structures to identify and overcome bottlenecks in carrier harvesting. Here, we present a theoretical and computational framework, Non-Equilibrium Scattering in Space and Energy (NESSE), to predict the spatial evolution of carrier energy distributions that com…
Spectroscopic studies of semiconductor quantum dots (SQDs) addressing the problem of non-radiative carrier losses is vital for the improvement in the efficiency of various light-emitting devices. Various designs of SQDs emitter like doping, forming core-shell and alloying has been attempted to suppress non-radiative recombination. In this article, we show that forming a hybrid with metal nanoparticles (MNP) having localized surface plasmon resonance overlapped with the emission spectrum of SQD, the non-radiative carrier loss via Auger recombination can be mitigated. Using steady-state and time…
Nonreciprocal plasmons in one-dimensional carbon nanostructures
Max-Born-Institut（马克斯·玻恩研究所）；Center for Nanophotonics, NWO Institute AMOLF（纳米光子学中心，NWO AMOLF研究所）；ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology（ICFO-光子科学研究所，巴塞罗那科学技术研究所）；ICREA-Institució Catalana de Recerca i Estudis Avançats（ICREA-加泰罗尼亚研究高级学院）；POLIMA—Center for Polariton-driven Light–Matter Interactions, University of Southern Denmark（POLIMA-极化激元驱动光物质相互作用中心，南丹麦大学）；Danish Institute for Advanced Study, University of Southern Denmark（丹麦高等研究院，南丹麦大学）
A plasmonic nanostructure conceived with periodic layers of a doped semiconductor and passive semiconductor is shown to generate spontaneously surface plasmon polaritons thanks to its periodic nature. The nanostructure is demonstrated to behave as an effective material modeled by a simple dielectric function of ionic-crystal type, and possesses a fully tunable photonic band gap, with widths exceeding 50%, in the region extending from mid-infra-red to Tera-Hertz.
Metal photoluminescence (MPL) originates from radiative recombination of photoexcited core holes and conduction band electrons. In metal nanostructures, MPL is enhanced due to the surface plasmon local field effect. We identify another essential process in plasmon-assisted MPL - excitation of Auger plasmons by core holes - that hinders MPL from small nanostructures. We develop a microscopic theory of plasmon-enhanced MPL that incorporates both plasmon-assisted enhancement and suppression mechanisms and derive the enhancement factor for MPL quantum efficiency. Our numerical calculations of MPL …
We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 micrometer. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy (STM) on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher…
Spin and angular momenta of light are important degrees of freedom in nanophotonics which control light propagation, optical forces and information encoding. Typically, optical angular momentum is generated using q-plates or spatial light modulators. Here, we show that graphene-supported plasmonic nanostructures with broken rotational symmetry provide a surprising spin to orbital angular momentum conversion, which can be continuously controlled by changing the electrochemical potential of graphene. Upon resonant illumination by a circularly polarized plane wave, a polygonal array of indium-tin…
The plasmonic chirality has drawn a lot of attention because of the tunable circular dichroism (CD) and the enhancement for the signal of chiral molecules. Different mechanisms have been proposed for explaining the plasmonic CD, however, a quantitative one like ab initio mechanism in chiral molecules is still unavailable. In this work, a mechanism similar to the chiral molecules is analyzed. The giant extrinsic circular dichroism of plasmonic splitting rectangle ring is quantitatively investigated theoretically. The interplay of electric and magnetic modes of the meta-structure is proposed to …
