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In this paper we study the behavior of a diatomic nonlinear one-dimensional lattice which represents the 〈1 1 1〉 direction of a zinc-blende three-dimensional crystal. In these nonlinear lattices are present intrinsic localized modes due to the anharmonicity. These modes lie in the vibrational gap between acoustic and optical linear spectrum. Considering a highly doped GaN semiconductor we examine the coexistence of the localized modes with the electronic plasma oscillations. We derive an expression for the plasmon electric field, we study the dynamics of the anharmonic lattice in presence of this electric field and we calculate the dielectric function of the coupled system. The zeroes of the dielectric function give the frequencies of the coupled modes.

Plasmonic film-nanoparticles coupled systems have had a renewed interest for the past 5 years both for the richness of the provided plasmonic modes and for their high technological potential. Many groups started to investigate the optical properties of film-nanoparticles coupled systems, as to whether the spacer layer thickness is tens of nanometers thick or goes down to a few nanometers or angstroms, even reaching contact. This article reviews the recent breakthroughs in the physical understanding of such coupled systems and the different systems where nanoparticles on top of the spacer layer are either isolated/random or form regular arrays. The potential for applications, especially as perfect absorbers or transmitters is also put into evidence.

In this paper we discuss the intrinsic localized modes of diatomic anharmonic chains for two different geometries, which simulate a row of a zinc-blende three-dimensional crystal or a row of an alkali-halide crystal. The modes are determined with two different potential models, using the full potential or the Taylor expansion truncated to fourth order. We obtain bulk modes and two kind of surface modes in the frequency gap between acoustical and optical phonons.

We present a theoretical investigation of the interaction of intrinsic localized modes with plasmons. The anharmonic localized modes for a 1D diatomic lattice are determined using a two-body potential which describes the interactions among particles in a zinc-blende structure material. The localized mode frequency is inside the gap between acoustic and optical phonons. Calculations have been performed for GaN because it has a large phonon gap, can be highly n-doped, and the plasma frequency of free carriers is in the range of phonon and intrinsic localized mode frequencies. To study the coupling we add to the equations of motion an electric field to simulate the plasmon. Solving the system we obtain the dynamical displacements pattern from which we evaluate the total polarization. From the polarization we determine the frequency of the combined mode for which the dielectric function is zero. In this investigation we have analysed both the case of small localized mode amplitudes and the case of larger amplitudes, obtaining different behaviour. In the first case the mixed mode has a frequency above the top of the optical branch, which can be explained in terms of the theory of the harmonic dielectric response of polar lattice vibrations. In the second case the coupled mode exists only for a finite slab, and its frequency is inside the phonon gap.

We present a detailed analysis of the interaction between intrinsic localized modes and plasmons in a doped polar semiconductor. The investigation has been performed for an anharmonic one-dimensional diatomic lattice with alternating interactions coupling successive neighbours. The system simulates a row of atoms in the direction of a III–V semiconductor. Specific calculations have been performed for GaN, because it has a large gap between the acoustic and optical phonon branches. The calculations of the intrinsic localized modes have been performed by using two-body potentials to describe the interactions. We have used the rotating wave approximation and we have found the intrinsic localized modes in the phonon gap. The interaction with the plasmon has been studied by adding to the equations of motion the alternating electric field which is related to the electron density of the plasmons. We obtain an expression for the electric dynamical polarization associated with the intrinsic localized modes and with the plasmons. We derive an expression for the dielectric function of the coupled system. The zeros of the dielectric function give the frequency of the combined modes. We have found two regimes in which combined modes are possible. One is related to small anharmonicity of the potential. The combined mode has a frequency above the top of the optical branch and can be explained in terms of the theory of the harmonic dielectric response of polar lattice vibrations. The second regime is related to high anharmonicity. The combined modes exist only for a finite slab. We show that on increasing the anharmonicity, i.e. the amplitude of the intrinsic localized mode, the width of the slab increases. The frequency of the combined mode is inside the phonon gap. We have also studied the dynamical stability of these modes.

In this paper we examine the existence of anharmonic localized modes using a full two-body potential to describe all interactions between particles in a zinc-blende-structure material, and we make a comparison with the results obtained with a nearest-neighbour force constant model that includes interactions up to quartic anharmonicity. We show that for amplitude up to a maximum displacement of the order of 0.25 A there are no appreciable differences between the two approaches, while for the largest amplitudes the force constant model gives unphysical results.