S. G. Tikhodeev

Symmetry breaking in a plasmonic metamaterial at optical wavelength

We numerically study the effect of structural asymmetry in a plasmonic metamaterial made from gold nanowires. It is reported that optically inactive (i.e., optically dark) particle plasmon modes of the symmetric wire lattice are immediately coupled to the radiation field, when a broken structural symmetry is introduced. Such higher order plasmon resonances are characterized by their subradiant nature. They generally reveal long lifetimes and distinct absorption losses. It is shown that the near-field interaction strongly determines these modes.

Matched coordinates and adaptive spatial resolution in the Fourier modal method

Several improvements have been introduced for the Fourier modal method in the last fifteen years. Among those, the formulation of the correct factorization rules and adaptive spatial resolution have been crucial steps towards a fast converging scheme, but an application to arbitrary two-dimensional shapes is quite complicated.We present a generalization of the scheme for non-trivial planar geometries using a covariant formulation of Maxwells equations and a matched coordinate system aligned along the interfaces of the structure that can be easily combined with adaptive spatial resolution. In addition, a symmetric application of Fourier factorization is discussed.

Polarization multistability of cavity polaritons.

New effects of polarization multistability and polarization hysteresis in a coherently driven polariton system in a semiconductor microcavity are predicted and theoretically analyzed. The multistability arises due to polarization-dependent polariton-polariton interactions and can be revealed in polarization resolved photoluminescence experiments. The pumping power required to observe this effect is 4 orders of magnitude lower than the characteristic pumping power in conventional bistable optical systems.

Optimized Design of Plasmonic MSM Photodetector

We present an optimized design for a plasmonic metal-semiconductor-metal photodetector with interdigitated electrodes with subwavelength dimensions and a single GaInNAs quantum well (QW) as an absorbing layer. The excitation of surface plasmons at the metal-semiconductor interface leads to a strong field enhancement near the metallic electrodes. This results in an increased absorption in the QW, allowing both fast electrical response of the photodetector and high quantum efficiencies. With a grating periodicity of 820 nm and electrode finger width of 460 nm a 16-fold increase in the absorption of p-polarized light in the QW is achieved in comparison to the case without electrodes.

Nonlinear dynamics of polariton scattering in semiconductor microcavity: Bistability vs. stimulated scattering

We investigate an unusual behavior of the parametric polariton scattering in a semiconductor microcavity (MC) under a strong cw resonant excitation: The maximum of the scattered signal above the threshold of stimulated parametric scattering does not shift along the microcavity lower polariton branch with the change of pump detuning or angle of incidence, but is fixed at normal direction. We show that such a behavior can be modelled numerically by a system of Maxwell and nonlinear Schrodinger equations for cavity polaritons and explained via the competition between the bistability of a driven nonlinear MC polariton and the instabilities of parametric polariton-polariton scattering.

Optical properties of photonic crystal slabs with an asymmetrical unit cell

Using the unitarity and reciprocity properties of the scattering matrix, we analyze the symmetry and resonant optical properties of the photonic crystal slabs (PCS) with non-trivial unit cell. We show that the reflectivity does not change upon the 180\ifmmode^\circ\else\textdegree\fi{}-rotation of the sample around the normal axis, even in PCS with asymmetric unit cell, whereas the transmissivity of the asymmetric PCS becomes asymmetrical if the diffraction or absorption are present. The PCS reflectivity peaks to unity near the quasiguided mode resonance for normal light incidence in the absence of diffraction, depolarization, and absorptive losses. For the oblique incidence the full reflectivity is reached only in symmetric PCS.

Theory of vibrational tunneling spectroscopy of adsorbates on metal surfaces

Abstract A theoretical model for studying elementary processes in vibrational scanning tunneling microscopy/spectroscopy is presented. General formulae for the elastic and inelastic tunneling currents are derived on the basis of the Anderson Hamiltonian coupled to a vibrational degree of freedom. Our treatment includes the vibrational damping due to electron–hole pair excitations. It is found that the non-equilibrium situation plays a crucial role for opening of the inelastic channel and excitations of adsorbate phonons. Elementary processes for both elastic and inelastic tunneling currents are clarified in a qualitative manner. The distribution function of adsorbate phonons is derived and may be of great importance for the understanding of the recently observed current-induced dynamical motions of adsorbates.

Near-field-induced tunability of surface plasmon polaritons in composite metallic nanostructures

We numerically study near‐field–induced coupling effects in metal nanowire‐based composite nanostructures. Our multi‐layer system is composed of individual gold nanowires supporting localized particle plasmons at optical wavelengths, and a spatially separated homogeneous silver slab supporting delocalized surface plasmons. We show that the localized plasmon modes of the composite structure, forming so‐called magnetic atoms, can be controlled over a large spectral range by changing the thickness of the nearby metal slab. The optical response of single‐wire and array‐based metallic structures are compared. Spectral shifts due to wire–mirror interaction as well as the coupling between localized and delocalized surface plasmon modes in a magnetic photonic crystal are demonstrated. The presented effects are important for the optimization of metal‐based nanodevices and may lead to the realization of metamaterials with novel plasmonic functionalities.

Contribution to a theory of vibrational scanning tunneling spectroscopy of adsorbates: Nonequilibrium Green's function approach

Abstract Formal theory of a phonon-assisted tunneling between a metal surface with an adsorbate and a metal scanning tip through an adsorbate (i.e., vibrational scanning tunneling spectroscopy (STS)) has been presented on the basis of the self-consistent nonequilibrium Keldyshs diagram technique. Within this approach, it is possible to take into account a finite lifetime of vibrational excitation, and the balance between elastic and opening inelastic tunneling channels. The relaxation of the vibrational degrees of freedom is included into the phonon Keldysh–Green function and plays a very important role both in the elastic and the inelastic tunneling through the adsorbate. The tunnel current (the total as well as the inelastic one) is calculated in terms of the one-particle nondiagonal substrate–adsorbate Keldysh–Greens function supplemented with the vibrational lifetime and filling factors of adsorbate orbital and phonons. The general expression of the inelastic tunnel current and conductance via the excitation of phonons is also presented in terms of the phonon occupation number and the phonon damping function in the stationary condition.

Polariton Effect in Distributed Feedback Microcavities

The excitonic and photonic states in distributed feedback (DFB) microcavities may strongly couple to form DFB cavity polaritons, provided that excitonic oscillator strength is large enough. In this paper we theoretically analyse the optical properties of DFB microcavities related to polariton effect. A numerical method based on scattering matrix formalism has been developed to solve the Maxwells equations for layered system with periodical patterning of layers. To incorporate polaritonic effect in our model we included the exciton poles in dielectric susceptibility of one of the patterned layers. Using this method we reproduce the characteristic features, demonstrated in recent experiments [Fujita et al.: Phys. Rev. B 57 (1998) 12428], such as anticrossing behavior of transmission dips in vicinity of the excitonic resonance and strong polarization dependence of their position and depth. ©2001 The Physical Society of Japan