META 2021, META'12

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Graphene and topological insulators for plasmonics, nanophotonics and photonic crystals
Yury Efremovich Lozovik

Last modified: 2011-12-14

Abstract


We discuss various applications of graphene and topological insulators as a constituents for for the elements of plasmonics, nanophotonics and photonic crystals.

Plasmon polaritons in a monolayer and bilayer doped graphene embedded in optical microcavity are discussed. The dispersion law for lower and upper cavity plasmon polaritons was obtained. Peculiarities of Rabi splitting for the system are analyzed; particularly, role of Dirac-like spinor (envelope) wave functions in graphene and corresponding angle factors were considered. Typical Rabi frequencies and frequencies of polaritons near polariton gap were estimated. The condition of existence of the lower pair of polaritons in the bilayer graphene system (corresponding to the antiphase plasmon mode) was obtained. The plasmon polaritons in the system can be used for high-speed information transfer in the THz region.

The influence of the optical contrast between the two media, located on opposite sides of graphene on the behavior of electromagnetic waves with TE and TM polarization is studied. It occurs that TE-polarized waves becomes leaky due to the increase of the optical contrast. In the case under consideration TE-mode frequency lies only in the window determined by the contrast. Analytical expressions describing the frequency range and extent of leakage depending on the contrast are obtained. The different characteristics of leaky modes - the wave vector, phase and group velocities, the characteristic length of leakage - are studied in detail. The sensitivity of TE-modes to changes in contrast is estimated. Near the frequency where the imaginary part of the conductivity of graphene vanishes, the very high sensitivity and very low detection limit are found. The effect considered can be used for design of highly sensitive optical sensors based on graphene. It is expected that they can essentially outperform modern plasmon resonance sensors.

The influence of metamaterial substrate on the TE-polarized electromagnetic waves in graphene is studied. It is found that TE-modes in graphene may exist not only in ordinary range but also for those frequencies where magnetic permeability of the metamaterial is negative. That can be used for detecting small concentrations of molecules absorbed on the graphene and excitation of TE-modes in graphene in terahertz range or lower. The advantage of TE-polarized electromagnetic waves in graphene in comparison with TM-polarized (plasmons, plasmon-polaritons) is that they propagates along the graphene layer with the velocity close to the velocity of light and have a weak damping.

The collective excitations in a helical electron liquid on a surface of three-dimensional topological insulator were studied . Electron in helical liquid obeys Dirac-like equation for massless particless and direction of its spin is strictly determined by its momentum. Due to this spin-momentum locking, collective excitations in the system

manifest themselves as coupled charge- and spin-density waves. The quantum field-theoretical description of spin-plasmons in helical liquid was developed and their properties and internal structure were studied. Value of spin polarization arising in the system with excited spin-plasmons was calculated. Also the scattering of spin-plasmons on magnetic and nonmagnetic impurities and external potentials is considered. It is shown that the scattering occurs mainly into two side lobes. Analogies with Dirac electron gas in graphene were discussed. According to the macroscopic Maxwell equations approach the dispersion laws of plasmon polaritons on the surface of topological insulator were obtained. The case of one-side and two-side excitation was considered. The condition of existence of the antiphase plasmon polaritons in the topological insulator film was obtained.

One-dimensional photonic crystal based on topological insulator (e.g., Bi2Se3 ) is studied. Due to the high bulk refractive index of Bi2Se3 it can be considered as high contrast photonic crystal. It is found that the spectrum of transmission of the system has very narrow frequency and angle peaks. The number of peaks on the angle scale depends on the number of photonic crystal layers. Possible application the photonic crystal for the design of optical sensors is considered. 

One-dimensional photonic crystal formed by a periodic array of graphene layers is considered. The photonic band structure and transmittance of such photonic crystal are calculated. The advantages of the graphene-based photonic crystal are discussed.

 

 


Keywords


plasmonics; photonic crystals; nanophotonicsp