Ebrahim Forati

Surface plasmon polaritons on soft-boundary graphene nanoribbons and their application in switching/demultiplexing

conductivity profile r(x) by finding the electrostatic charge distribution q(x) on the graphene sheet from Laplace’s equation, leading to the chemical potential lcðxÞ and the conductivity via the Kubo formula. It was shown that the ridged structure does indeed allow for the formation of a channel in the vicinity of the ridge for SPP propagation using a single bias, but that the resulting boundary has, as expected, a softened profile (i.e., a soft boundary (SB)) wherein the conductivity is not constant. The work 27 was concerned with the properties of the soft boundary and resulting channel, and the current distribution of the fundamental SPP mode. In this work we consider the various other modes that can propagate along the SB channel, including higher-order modes and edge modes. In particular, we show that unlike the HB case, for a soft boundary the higher-order modes have no apparent low-frequency/long-wavelength cutoff, although as frequency is lowered modal energy tends to spread out laterally along the effectively wider channel. We also show that lowloss edge modes can propagate for which the location where energy is concentrated can be controlled electronically. We then consider two applications of the structure, as a plasmonic voltage-controlled switch and a frequency demultiplexer. Fig. 2 shows the conductivity profile r(x) of the graphene sheet for a representative set of geometrical and FIG. 1. Graphene sheet gated with a ridged, perfect electrically-conducting (PEC) ground plane for the electrostatic bias, forming a soft-boundary graphene nanoribbon. The red area depicts the SPP channel having Im rðxÞ 0 and SPP propagation is prohibited.A graphene sheet gated with a ridged ground plane, creating a soft-boundary (SB) graphene nanoribbon, is considered. By adjusting the ridge parameters and bias voltage a channel can be created on the graphene which can guide TM surface plasmon polaritons (SPP). Two types of modes are found; fundemental and higher-order modes with no apparent cutoff frequency and with energy distributed over the created channel, and edge modes with energy concentrated at the soft-boundary edge. Dispersion curves, electric near-field patterns, and current distributions of these modes are determined. Since the location where energy is concentrated in the edge modes can be easily controlled electronically by the bias voltage and frequency, the edge-mode phenomena is used to propose a novel voltage controlled plasmonic switch and a plasmonic frequency demultiplexer. ∗To whom correspondence should be addressed 1 ar X iv :1 30 6. 31 43 v4 [ ph ys ic s. op tic s] 2 4 Se p 20 13

Planar hyperlens based on a modulated graphene monolayer

The canalization of terahertz surface plasmon polaritons using a modulated graphene monolayer is investigated for subwavelength imaging. An anisotropic surface conductivity formed by a set of parallel nanoribbons with alternating positive and negative imaginary conductivities is used to realize the canalization regime required for hyperlensing. The ribbons are narrow compared to the wavelength, and are created electronically by gating a graphene layer over a corrugated ground plane. Good quality canalization of surface plasmon polaritons is shown in the terahertz even in the presence of realistic loss in graphene, with relevant implications for subwavelength imaging applications.

The Effect of Sample Holder Geometry on Electromagnetic Heating of Nanoparticle and NaCl Solutions at 13.56 MHz

Electromagnetic absorption and subsequent heating of nanoparticle solutions and simple NaCl ionic solutions is examined for biomedical applications in the radiofrequency range at 13.56 MHz. It is shown via both theory and experiment that for in vitro measurements the shape of the solution container plays a major role in absorption and heating.

Modeling of Spatially-Dispersive Wire Media: Transport Representation, Comparison With Natural Materials, and Additional Boundary Conditions

Natural and artificial wire materials exhibiting spatial dispersion are considered using a transport (drift-diffusion) model. The connection between drift-diffusion and electron transport in natural materials is highlighted, and then applied to various forms of wire media, leading to the definition of effective conductivity and diffusion parameters that characterize the material. It is shown that the effective material parameters lead to a Debye length that provides a quantitative measure of the strength of spatial dispersion for wire mediums. Further, it is shown that Pekars additional boundary condition applies in many instances to natural materials as well as artificial wire media, and can be derived from elementary electromagnetics.

Soft-boundary graphene nanoribbon formed by a graphene sheet above a perturbed ground plane: conductivity profile and SPP modal current distribution

An infinite sheet of graphene lying above a perturbed ground plane is studied. The perturbation is a two-dimensional ridge, and a bias voltage is applied between the graphene and the ground plane, resulting in a graphene nanoribbon-like structure with a soft boundary (SB). The spatial distribution of the graphene conductivity forming the SB is studied as a function of the ridge parameters and the bias voltage. The current distribution of the fundamental transverse magnetic surface plasmon polariton (SPP) is considered. The effect of the ridge parameters and shape of the SB on the current distributions are investigated, and the conditions are studied under which the mode remains confined to the vicinity of the ridge region.

Enhanced Faraday rotation in hybrid magneto-optical metamaterial structure of bismuth-substituted-iron-garnet with embedded-gold-wires

We propose an alternative class of magneto-optical metamaterials offering enhanced angle of rotation in polarization compared to pure magneto-optical materials. In this approach, the permittivity tensor of a magneto-optical material is tailored by embedded wire meshes. We show that the angle of rotation in the magneto-optical metamaterial can be enhanced up to 9 times compared to pure magneto-optical material alone, while the polarization extinction ratio remains below −20dB over more than 2 THz bandwidth and the attenuation coefficient is approximately 1.5dB μm−1.

Photoemission-based microelectronic devices

The vast majority of modern microelectronic devices rely on carriers within semiconductors due to their integrability. Therefore, the performance of these devices is limited due to natural semiconductor properties such as band gap and electron velocity. Replacing the semiconductor channel in conventional microelectronic devices with a gas or vacuum channel may scale their speed, wavelength and power beyond what is available today. However, liberating electrons into gas/vacuum in a practical microelectronic device is quite challenging. It often requires heating, applying high voltages, or using lasers with short wavelengths or high powers. Here, we show that the interaction between an engineered resonant surface and a low-power infrared laser can cause enough photoemission via electron tunnelling to implement feasible microelectronic devices such as transistors, switches and modulators. The proposed photoemission-based devices benefit from the advantages of gas-plasma/vacuum electronic devices while preserving the integrability of semiconductor-based devices.

A New Formulation of Pocklington's Equation for Thin Wires Using the Exact Kernel

Pocklingtons integro-differential equation for thin wires with the exact kernel is reformulated using a second derivative formula for improper integrals. This allows for analytical evaluation of the second derivatives, resulting in a pure integral equation, in a similar manner to what is done when using the approximate kernel. However, as opposed to using the approximate kernel, the resulting integral equation developed here is numerically stable even with a simple pulse function/point matching solution. Good convergence for the current is obtained using pulse functions, and the severe unphysical oscillations of the current that are encountered when using pulse functions with the approximate kernel are avoided.

Graphene as a tunable THz reservoir for shaping the Mollow triplet of an artificial atom via plasmonic effects

(Received 29 April 2014; revised manuscript received 30 June 2014; published 12 August 2014)Using a realistic quantum master equation, we show that the resonance fluorescence spectra of a two-levelartificialatom(quantumdot)canbetunedbyadjustingitsphotoniclocaldensityofstatesviabiasingoneormoregraphene monolayers. The structured photon reservoir is included using a photon Green function theory whichfully accounts for the loss and dispersion. The field-driven Mollow triplet spectrum can be actively controlled bythe graphene bias in the THz frequency regime. We also consider the effect of a dielectric support environmentand multiple graphene layers on the emitted fluorescence. Finally, thermal bath effects are considered and areshown to be important for low THz frequencies.DOI: 10.1103/PhysRevB.90.085414 PACS number(s): 78

An Epsilon-Near-Zero Total-Internal-Reflection Metamaterial Antenna

The total-internal-reflection (TIR) principle and the concept of an epsilon-near-zero (ENZ) material are combined to form an antenna exhibiting sum and difference patterns with good impedance properties. The ENZ material has been realized using a uniaxial wire medium (WM) metamaterial, and the departure from the behavior of an ideal ENZ material is discussed. The radiation pattern of the fabricated antennas has been measured and compared with simulation results.