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Kurter C.,University of Maryland University College | Tassin P.,Iowa State University | Tassin P.,Vrije Universiteit Brussel | Zhuravel A.P.,Ukrainian Academy of Sciences | And 7 more authors.
Applied Physics Letters | Year: 2012

We demonstrate a nonlinear metamaterial that can be switched between low and high transmission by controlling the power level of the incident beam. The origin of this nonlinear response is the superconducting Nb thin film employed in the metamaterial structure. We show that with moderate RF power of about 22 dBm it is possible to quench the superconducting state as a result of extremely strong current densities at the corners of the metamaterial's split-ring resonators. We measure a transmission contrast of 10 dB and a change in group delay of 70 ns between the low and high power states. © 2012 American Institute of Physics.


Zou Y.,Iowa State University | Zou Y.,Hunan University | Tassin P.,Iowa State University | Koschny T.,Iowa State University | And 2 more authors.
Optics Express | Year: 2012

We have recently shown that graphene is unsuitable to replace metals in the current-carrying elements of metamaterials. At the other hand, experiments have demonstrated that a layer of graphene can modify the optical response of a metal-based metamaterial. Here we study this electromagnetic interaction between metamaterials and graphene. We show that the weak optical response of graphene can be modified dramatically by coupling to the strong resonant fields in metallic structures. A crucial element determining the interaction strength is the orientation of the resonant fields. If the resonant electric field is predominantly parallel to the graphene sheet (e.g., in a complementary split-ring metamaterial), the metamaterial's resonance can be strongly damped. If the resonant field is predominantly perpendicular to the graphene sheet (e.g., in a wire-pair metamaterial), no significant interaction exists. © 2012 Optical Society of America.


Tassin P.,Iowa State University | Zhang L.,Iowa State University | Zhao R.,Iowa State University | Zhao R.,Imperial College London | And 4 more authors.
Physical Review Letters | Year: 2012

Several classical analogues of electromagnetically induced transparency in metamaterials have been demonstrated. A simple two-resonator model can describe their absorption spectrum qualitatively, but fails to provide information about the scattering properties-e.g., transmission and group delay. Here we develop an alternative model that rigorously includes the coupling of the radiative resonator to the external electromagnetic fields. This radiating two-oscillator model can describe both the absorption spectrum and the scattering parameters quantitatively. The model also predicts metamaterials with a narrow spectral feature in the absorption larger than the background absorption of the radiative element. This classical analogue of electromagnetically induced absorption is shown to occur when both the dissipative loss of the radiative resonator and the coupling strength are small. These predictions are subsequently demonstrated in experiments. © 2012 American Physical Society.


Ginis V.,Vrije Universiteit Brussel | Tassin P.,Chalmers University of Technology | Koschny T.,Iowa State University | Soukoulis C.M.,Iowa State University | Soukoulis C.M.,Institute of Electronic Structure and Lasers IESL
Applied Physics Letters | Year: 2016

Metasurfaces allow for advanced manipulation of optical signals by imposing phase discontinuities across flat interfaces. Unfortunately, these phase shifts remain restricted to values between 0 and 2π, limiting the delay-bandwidth product of such sheets. Here, we develop an analytical tool to design metasurfaces that mimic three-dimensional materials of arbitrary thickness. In this way, we demonstrate how large phase discontinuities can be realized by combining several subwavelength Lorentzian resonances in the unit cell of the surface. Our methods open up the temporal response of metasurfaces and may lead to the construction of metasurfaces with a plethora of new optical functions. © 2016 AIP Publishing LLC.


Jain A.,Iowa State University | Tassin P.,Iowa State University | Koschny T.,Iowa State University | Soukoulis C.M.,Iowa State University | Soukoulis C.M.,Institute of Electronic Structure and Lasers IESL
Physical Review Letters | Year: 2014

Metamaterials - or artificial electromagnetic materials - can create media with properties unattainable in nature, but mitigating dissipation is a key challenge for their further development. Here, we demonstrate a low-loss metamaterial by exploiting dark bound states in dielectric inclusions coupled to the external waves by small nonresonant metallic antennas. We experimentally demonstrate a dispersion-engineered metamaterial based on a meta-atom made from alumina, and we show that its resonance has a much larger quality factor than metal-based meta-atoms. Finally, we show that our dielectric meta-atom can be used to create sheet metamaterials with negative permittivity or permeability. © 2014 American Physical Society.


Chatzakis I.,Iowa State University | Tassin P.,Iowa State University | Luo L.,Iowa State University | Shen N.-H.,Iowa State University | And 5 more authors.
Applied Physics Letters | Year: 2013

Emerging technology based on artificial materials containing metallic structures has raised the prospect for unprecedented control of terahertz waves. The functionality of these devices is static by the very nature of their metallic composition, although some degree of tunability can be achieved by incorporating electrically biased semiconductors. Here, we demonstrate a photonic structure by projecting the optical image of a metal mask onto a thin GaAs substrate using a femtosecond pulsed laser source. We show that the resulting high-contrast pattern of photo-excited carriers can create diffractive elements operating in transmission, potentially providing a route to terahertz components with reconfigurable functionality. © 2013 AIP Publishing LLC.


Tassin P.,Iowa State University | Koschny T.,Iowa State University | Kafesaki M.,Institute of Electronic Structure and Lasers IESL | Soukoulis C.M.,Iowa State University | Soukoulis C.M.,Institute of Electronic Structure and Lasers IESL
Nature Photonics | Year: 2012

Recent advancements in metamaterials and plasmonics have promised a number of exciting applications, in particular at terahertz and optical frequencies. Unfortunately, the noble metals used in these photonic structures are not particularly good conductors at high frequencies, resulting in significant dissipative loss. Here, we address the question of what is a good conductor for metamaterials and plasmonics. For resonant metamaterials, we develop a figure-of-merit for conductors that allows for a straightforward classification of conducting materials according to the resulting dissipative loss in the metamaterial. Application of our method predicts that graphene and high-T c superconductors are not viable alternatives for metals in metamaterials. We also provide an overview of a number of transition metals, alkali metals and transparent conducting oxides. For plasmonic systems, we predict that graphene and high-Tc superconductors cannot outperform gold as a platform for surface plasmon polaritons, because graphene has a smaller propagation length-to-wavelength ratio. © 2012 Macmillan Publishers Limited. All rights reserved.


Ginis V.,Vrije Universiteit Brussel | Tassin P.,Iowa State University | Danckaert J.,Vrije Universiteit Brussel | Soukoulis C.M.,Iowa State University | And 2 more authors.
New Journal of Physics | Year: 2012

We investigate the potential of transformation optics for the design of novel electromagnetic cavities. First, we determine the dispersion relation of bound modes in a device performing an arbitrary radial coordinate transformation and we discuss a number of such cavity structures. Subsequently, we generalize our study to media that implement azimuthal transformations, and show that such transformations can manipulate the azimuthal mode number. Finally, we discuss how the combination of radial and azimuthal coordinate transformations allows for perfect confinement of subwavelength modes inside a cavity consisting of right-handed materials only. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Zhang L.,Iowa State University | Koschny T.,Iowa State University | Soukoulis C.M.,Iowa State University | Soukoulis C.M.,Institute of Electronic Structure and Lasers IESL
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Metamaterials are patterned metallic structures which permit access to a novel electromagnetic response, negative index of refraction, impossible to achieve with naturally occurring materials. Using the Babinet principle, the complementary split ring resonator (SRR) is etched in a metallic plate to provide negative ε, with perpendicular direction. Here we propose a new design, etched in a metallic plate to provide negative magnetic permeability μ, with perpendicular direction. The combined electromagnetic response of this planar metamaterial, where the negative μ comes from the aperture and the negative ε from the remainder of the continuous metallic plate, allows achievement of a double negative index metamaterial (NIM) with only one metasurface and strong transmission. These designs can be used to fabricate NIMs at microwave and optical wavelengths and three-dimensional metamaterials. © 2013 American Physical Society.


Tassin P.,Iowa State University | Koschny T.,Iowa State University | Soukoulis C.M.,Iowa State University | Soukoulis C.M.,Institute of Electronic Structure and Lasers IESL
Physica B: Condensed Matter | Year: 2012

An important tool in the field of metamaterials is the extraction of effective material parameters from simulated or measured scattering parameters of a sample. Here we discuss a retrieval method for thin-film structures that can be approximated by a two-dimensional scattering sheet. We determine the effective sheet conductivity from the scattering parameters and we point out the importance of the magnetic sheet current to avoid an overdetermined inversion problem. Subsequently, we present two applications of the sheet retrieval method. First, we determine the effective sheet conductivity of thin silver films and we compare the resulting conductivities with the sheet conductivity of graphene. Second, we apply the method to a cut-wire metamaterial with an electric dipole resonance. The method is valid for thin-film structures such as two-dimensional metamaterials and frequency-selective surfaces and can be easily generalized for anisotropic or chiral media. © 2012 Elsevier B.V.

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