Nikitas Papasimakis

Sharp Trapped-Mode Resonances in Planar Metamaterials with a Broken Structural Symmetry

We report that a resonance response with a very high quality factor can be achieved in a planar metamaterial by introducing symmetry breaking in the shape of its structural elements, which enables excitation of trapped modes, i.e., modes that are weakly coupled to free space.

Metamaterial Analog of Electromagnetically Induced Transparency

We demonstrate a classical analog of electromagnetically induced transparency in a planar metamaterial. We show that pulses propagating through such metamaterials experience considerable delay. The thickness of the structure along the direction of wave propagation is much smaller than the wavelength, which allows successive stacking of multiple metamaterial slabs leading to increased transmission and bandwidth.

Coherent meta-materials and the lasing spaser

In 2003 Bergman and Stockman introduced the spaser, a quantum amplifier of surface plasmons by stimulated emission of radiation. They argued that, by exploiting a metal/dielectric composite medium, it should be possible to construct a nano-device, where a strong coherent field is built up in a spatial region much smaller than the wavelength. It was suggested that V-shaped metallic inclusions, combined with a collection of semiconductor quantum dots could lead to a realization of the spaser. Here we introduce a further development of the spaser concept. We show that by combining the metamaterial and spaser ideas one can create a planar narrow-diversion coherent source of electromagnetic radiation that is fuelled by plasmonic oscillations. We argue that two-dimensional arrays of a certain class of plasmonic resonators supporting high-Q current excitations belong to a new category of coherent metamaterials that provide an intriguing opportunity to create a spatially and temporally coherent laser source, the Lasing Spaser.

Toroidal Dipolar Response in a Metamaterial

Making a Point with Metamaterials A long-predicted electromagnetic excitation, the toroidal moment (or anapole), is associated with toroidal shape and current flow within a structure and has been implicated in nuclear and particle physics. This distinct family of electromagnetic excitations has not been observed directly because they are masked by much stronger electric and magnetic multipoles. Kaelberer et al. (p. 1510, published online 4 November) have developed a metamaterial structure based on stacked loops of inverted split-ring resonators (“metamolecules”) whose response under excitation is consistent with the existence of a toroidal moment. The metamaterial is designed so that both the electric and magnetic dipole moments induced by an incident electromagnetic wave are suppressed, while the toroidal response is isolated and resonantly enhanced to a detectable level. A material that embeds metal wire loops in a dielectric has properties consistent with an exotic electromagnetic excitation. Toroidal multipoles are fundamental electromagnetic excitations different from those associated with the familiar charge and magnetic multipoles. They have been held responsible for parity violation in nuclear and particle physics, but direct evidence of their existence in classical electrodynamics has remained elusive. We report on the observation of a resonant electromagnetic response in an artificially engineered medium, or metamaterial, that cannot be attributed to magnetic or charge multipoles and can only be explained by the existence of a toroidal dipole. Our direct experimental evidence of the toroidal response brings attention to the often ignored electromagnetic interactions involving toroidal multipoles, which could be present in naturally occurring systems, especially at the macromolecule level, where toroidal symmetry is ubiquitous.

Metamaterial with polarization and direction insensitive resonant transmission response mimicking electromagnetically induced transparency

We report on a planar metamaterial, the resonant transmission frequency of which does not depend on the polarization and angle of incidence of electromagnetic waves. The resonance results from the excitation of high-Q antisymmetric trapped current mode and shows sharp phase dispersion characteristic to Fano-type resonances of the electromagnetically induced transparency phenomenon.

Graphene in a photonic metamaterial

We demonstrate a photonic metamaterial that shows extraordinary sensitivity to the presence of a single atomic layer of graphene on its surface. Metamaterials optical transmission increases multi-fold at the resonance frequency linked to the Fano-type plasmonic mode supported by the periodic metallic nanostructure. The experiments were performed with chemical vapor deposited (CVD) graphene covering a number of size-scaled metamaterial samples with plasmonic modes at different frequencies ranging from 167 to 187 Thz.

Spectral Collapse in Ensembles of Metamolecules

We report on the first direct experimental demonstration of a collective phenomenon in metamaterials: spectral line collapse with an increasing number of unit cell resonators (metamolecules). This effect, which is crucial for achieving a lasing spaser, a coherent source of optical radiation fuelled by coherent plasmonic oscillations in metamaterials, is linked to the suppression of radiation losses in periodic arrays. We experimentally demonstrate spectral line collapse at microwave, terahertz and optical frequencies.

Carbon nanotubes in a photonic metamaterial

Hybridization of single-walled carbon nanotubes with plasmonic metamaterials leads to photonic media with an exceptionally strong ultrafast nonlinearity. This behavior is underpinned by strong coupling of the nanotube excitonic response to the weakly radiating Fano-type resonant plasmonic modes that can be tailored by metamaterial design.

Surface-Enhanced Infrared Spectroscopy Using Metal Oxide Plasmonic Antenna Arrays

We successfully demonstrate surface-enhanced infrared spectroscopy using arrays of indium tin oxide (ITO) plasmonic nanoantennas. The ITO antennas show a strongly reduced plasmon wavelength, which holds promise for ultracompact antenna arrays and extremely subwavelength metamaterials. The strong plasmon confinement and reduced antenna cross section allows ITO antennas to be integrated at extremely high densities with no loss in performance due to long-range transverse interactions. By further reducing the spacing of antennas in the arrays, we access the regime of plasmonic near field coupling where the response is enhanced for both Au and ITO devices. Ultracompact ITO antennas with high spatial and spectral selectivity in spectroscopic applications offer a viable new platform for infrared plasmonics, which may be combined with other functionalities of these versatile materials in devices.

Metamaterial-induced transparency: sharp fano resonances and slow light

Inspired by the study of atomic resonances, researchers have developed a new type of metamaterial. Their work paves the way toward compact delay lines and slow-light devices.