Showing papers by "John B. Pendry published in 2016"
TL;DR: A tunable plasmonic metasurface is demonstrated by considering a graphene sheet subject to a periodically patterned doping level, and an efficient control of THz radiation for one polarization is shown.
Abstract: We demonstrate a tunable plasmonic metasurface by considering a graphene sheet subject to a periodically patterned doping level. The unique optical properties of graphene result in electrically tunable plasmons that allow for extreme confinement of electromagnetic energy in the technologically significant regime of THz frequencies. Here, we add an extra degree of freedom by using graphene as a metasurface, proposing to dope it with an electrical gate patterned in the micron or submicron scale. By extracting the effective conductivity of the sheet, we characterize metasurfaces periodically modulated along one or two directions. In the first case, and making use of the analytical insight provided by transformation optics, we show an efficient control of THz radiation for one polarization. In the second case, we demonstrate a metasurface with an isotropic response that is independent of wave polarization and orientation.
65 citations
TL;DR: In this article, the contribution of phonons to heat transfer mediated by van der Waals forces is investigated. But the results show a more dramatic decay with separation than previous work.
Abstract: With increasing interest in nanotechnology, the question arises of how heat is exchanged between materials separated by only a few nanometers of vacuum. Here, we present calculations of the contribution of phonons to heat transfer mediated by van der Waals forces and compare the results to other mechanisms such as coupling through near field fluctuations. Our results show a more dramatic decay with separation than previous work.
57 citations
TL;DR: In this article, the authors studied subwavelength gratings for coupling into graphene plasmons by means of an analytical model based on transformation optics that is not limited to very shallow gratings.
Abstract: Here we study subwavelength gratings for coupling into graphene plasmons by means of an analytical model based on transformation optics that is not limited to very shallow gratings. We consider gratings that consist of a periodic modulation of the charge density in the graphene sheet, and gratings formed by this conductivity modulation together with a dielectric grating placed in close vicinity of the graphene. Explicit expressions for the dispersion relation of the plasmon polaritons supported by the system, and reflectance and transmittance under plane wave illumination are given. We discuss the conditions for maximising the coupling between incident radiation and plasmons in the graphene, finding the optimal modulation strength for a conductivity grating.
38 citations
TL;DR: The van der Waals force originates from the electromagnetic interaction between quantum fluctuation-induced charges and has a wide range of applications in surface related phenomena like adhesion, friction, and colloidal stability as discussed by the authors.
Abstract: The van der Waals force originates from the electromagnetic interaction between quantum fluctuation-induced charges. It is a ubiquitous but subtle force which plays an important role and has a wide range of applications in surface related phenomena like adhesion, friction, and colloidal stability. Calculating the van der Waals force between closely spaced metallic nanoparticles is very challenging due to the strong concentration of electromagnetic fields at the nanometric gap. Especially, at such a small length scale, the macroscopic description of the dielectric properties no longer suffices. The diffuse nonlocal nature of the induced surface electrons which are smeared out near the boundary has to be considered. Here, we review the recent progress on using three-dimensional transformation optics to study the van der Waals forces between closely spaced nanostructures. Through mapping a seemingly asymmetric system to a more symmetric counterpart, transformation optics enables us to look into the behavior of van der Waals forces at extreme length scales, where the effect of nonlocality is found to dramatically weaken the van der Waals interactions.
24 citations
16 citations
TL;DR: A new method based on transformation optics that allows to calculate the quasistatic frequency- and time-domain response of plasmonic particles under electron beam excitation is introduced.
Abstract: Electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) play a pivotal role in many of the cutting edge experiments in plasmonics. EELS and CL experiments are usually supported by numerical simulations, which—though accurate—may not provide as much physical insight as analytical calculations do. Fully analytical solutions to EELS and CL systems in plasmonics are rare and difficult to obtain. This paper aims to narrow this gap by introducing a new method based on transformation optics that allows to calculate the quasistatic frequency- and time-domain response of plasmonic particles under electron beam excitation. We study a nonconcentric annulus (and ellipse in the Supporting Information) as an example.
11 citations
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TL;DR: In this article, a new type of metamaterial structure composing of several interpenetrating wire meshes was proposed and investigated, and calculated band structures showed that they exhibit index ellipsoids locating at nonzero k-point in long wavelength limit.
Abstract: We propose and investigate a new type of metamaterial structure composing of several interpenetrating wire meshes. Calculated band structures show that they exhibit index ellipsoids locating at nonzero k-point in long wavelength limit. We can comprehend these quasistatic modes by Poison's equation and find these modes do not rely on the detailed geometry of the wires but the connectivities of the wires. We can engineer the locations of index ellipsoid by designing the connectivities of the wire meshes.
11 citations
TL;DR: An alternative "quantum metamaterials" (QM) approach that uses materials structured at the nanoscale, i.e., comparable to an electron wavelength, to generate structures with a highly elliptical isofrequency dispersion characteristic that circumvents this loss problem is demonstrated.
Abstract: Recently, so-called “superlenses”, made from metamaterials that are structured on a length scale much less than an optical wavelength, have shown impressive diffraction-beating image resolution, but they use materials with negative dielectric responses, and they absorb much of the light in a way that seriously degrades both the resolution and brightness of the image. Here we demonstrate an alternative “quantum metamaterials” (QM) approach that uses materials structured at the nanoscale, i.e., comparable to an electron wavelength. This allows us to use quantum mechanical design principles to generate structures with a highly elliptical isofrequency dispersion characteristic that circumvents this loss problem. The physics of the loss improvement is analyzed analytically and the QM superlens subdiffraction imaging is modeled numerically, with a finite-element method. Finally, we demonstrate a working QM superlens device, utilizing intersubband transitions between the confined electron states in a III–V semic...
11 citations
TL;DR: In this article, an ultrathin plasmonic grating made of a gold grating covered by a thin flat layer of gold was proposed to achieve bianisotropy at visible wavelengths.
Abstract: We present a simple design to achieve bianisotropy at visible wavelengths: an ultrathin plasmonic grating made of a gold grating covered by a thin flat layer of gold. We show experimentally and through simulations that the grating exhibits magnetoelectric coupling and features asymmetric reflection and absorption, all that with a device thickness of a tenth of the operating wavelength. We compared the spectral results and retrieved the effective material parameters of different polarizations and devices. We show that both asymmetry and strong coupling between the incoming light and the optically interacting surfaces are required for obtaining asymmetric optical behavior in metasurfaces.
11 citations
TL;DR: In this article, an ultrathin plasmonic grating made of a gold grating covered by a thin flat layer of gold was proposed to achieve bianisotropy at visible wavelengths.
Abstract: We present a simple design to achieve bianisotropy at visible wavelengths: an ultrathin plasmonic grating made of a gold grating covered by a thin flat layer of gold. We show experimentally and through simulations that the grating exhibits magneto-electric coupling and features asymmetric reflection and absorption, all that with a device thickness of a tenth of the operating wavelength. We compared the spectral results and retrieved the effective material parameters of different polarizations and devices. We show that both asymmetry and strong coupling between the incoming light and the optically interacting surfaces are required for obtaining asymmetric optical behavior in metasurfaces.
10 citations
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TL;DR: In this paper, a method based on transformation optics is proposed to characterize and model the EELS problems of nanoparticles of complex geometries, where the frequency and time domain responses under electron beam excitations are derived.
Abstract: As the continual experimental advances made in Electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) open the door to practical exploitations of plasmonic effects in metal nanoparticles, there is an increasing need for precise interpretation and guidance of such experiments. Numerical simulations are available but lack physical insight, while traditional analytical approaches are rare and limited to studying specific, simple structures. Here, we propose a versatile and efficient method based on transformation optics which can fully characterize and model the EELS problems of nanoparticles of complex geometries. Detailed discussions are given on 2D and 3D nanoparticle dimers, where the frequency and time domain responses under electron beam excitations are derived.
01 Aug 2016
TL;DR: Graphene can be biased by electrical gating or by chemical doping, which modifies its Fermi level and enables the existence of surface plasmons propagating along graphene as discussed by the authors.
Abstract: Graphene can be biased by electrical gating or by chemical doping, which modifies its Fermi level and enables the existence of surface plasmons propagating along graphene. These surface plasmons, because of the two-dimensional (2D) nature of this material, have very short wavelengths and extreme out-of-plane confinement. Graphene plasmons feature in the THz regime with relatively low losses, where the plasmonic response of metals is weak. These facts, added to the important ingredient of tunability with external bias, make graphene a very suitable platform for the design of plasmonic metasurfaces in the THz regime. Metasurfaces, which are the 2D counterpart of metamaterials, consist of a planar arrangement of resonant subwavelengthsize building blocks. By appropriately them, metasurfaces provide an ultrathin platform for manipulating electromagnetic waves, and they have shown novel phenomena and applications as from broadband light bending and anomalous reflection and refraction.
TL;DR: In this article, the conditions for maximising the coupling between incident radiation and plasmons in the graphene, finding the optimal modulation strength for a conductivity grating was discussed, and explicit expressions for the dispersion relation of the plasmon po- laritons supported by the system were given.
Abstract: Here we study subwavelength gratings for coupling into graphene plasmons by means of an an- alytical model based on transformation optics that is not limited to very shallow gratings. We consider gratings that consist of a periodic modulation of the charge density in the graphene sheet, and gratings formed by this conductivity modulation together with a dielectric grating placed in close vicinity of the graphene. Explicit expressions for the dispersion relation of the plasmon po- laritons supported by the system, and reflectance and transmittance under plane wave illumination are given. We discuss the conditions for maximising the coupling between incident radiation and plasmons in the graphene, finding the optimal modulation strength for a conductivity grating.
01 Aug 2016
TL;DR: In this paper, a new method based on transformation optics was proposed to analyze the electromagnetic response of plasmonic particles under electron beam excitation, and the results for the electron energy loss and photon scattering spectra of a 2-d crescent and 3-d dimer were presented.
Abstract: Electron energy loss spectroscopy is one of the most important and versatile tools for experiments at the frontier of plasmonics research. In this short paper, we present a new method based on Transformation optics to analyze the electromagnetic response of plasmonic particles under electron beam excitation. We present analytical results for the electron energy loss and photon scattering spectra of a 2-d crescent and 3-d dimer, as well as their time-domain response. We believe this method can support and guide future EELS experiments in plasmonics and beyond.
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TL;DR: In this article, the theoretical derivation for phonon transmission is revisited and extended to the case of two bodies made of different materials separated by a vacuum gap, and hence the heat transfer, for commonly used materials in the micro and nano-electromechanical industry are calculated and compared with the calculation of conduction heat transfer through air for small gaps.
Abstract: Phonons (collective atomic vibrations in solids) are more effective in transporting heat than photons This is the reason why the conduction mode of heat transport in nonmetals (mediated by phonons) is dominant compared to the radiation mode of heat transport (mediated by photons) However, since phonons are unable to traverse a vacuum gap (unlike photons) it is commonly believed that two bodies separated by a gap cannot exchange heat via phonons Recently, a mechanism was proposed by which phonons can transport heat across a vacuum gap - through Van der Waals interaction between two bodies with gap less than wavelength of light Such heat transfer mechanisms are highly relevant for heating (and cooling) of nanostructures; the heating of the flying heads in magnetic storage disks is a case in point Here, the theoretical derivation for modeling phonon transmission is revisited and extended to the case of two bodies made of different materials separated by a vacuum gap Magnitudes of phonon transmission, and hence the heat transfer, for commonly used materials in the micro and nano-electromechanical industry are calculated and compared with the calculation of conduction heat transfer through air for small gaps