Nonradiative Polaritons Research Articles

Effect of quantizing magnetic field on the spectrum and damping of polaritons in double two-dimensional electronic systems

Nonradiative (surface and bulk) polaritons in a semiconductor structure composed of two heterojunctions GaAs/AlxGa1−x As are investigated under the integer quantum Hall effect (IQHE) conditions. The dispersive, polarization, and energy characteristics of these polaritons are determined including energy dissipation in the two-dimensional electron semiconductor layers. The phase and group velocities of surface and bulk polaritons are shown to be quantized under the IQHE conditions. It is found that resonance coupling of two surface polariton modes may occur in double GaAs/AlxGa1−x As heterojunctions. Possible experimental observation of nonradiative polaritons is discussed.

Effect of dissipation on the properties of surface polaritons in GaAs/AlGaAs heterojunctions in a quantizing magnetic field

A study is reported of nonradiative surface and bulk polaritons in GaAs/AlxGa1−x As real heterojunctions under conditions favoring integer-quantum Hall effect (IQHE) and in the presence of dissipation in a two-dimensional electron layer. The conditions of their existence, the spectrum, and damping have been determined. It is shown that under IQHE conditions all aspects of surface and bulk polaritons are quantized. It is found that, as the wave number is varied, surface and bulk polaritons can transform continuously into one another. The possibilities of experimental observation of nonradiative polaritons are discussed.

Superradiance of polaritons in finite one-dimensional crystals of increasing length: Passage from a dimer to an infinite crystal

Solutions of the dispersion equations for polariton states in finite one-dimensional crystals of arbitrary length are obtained. The appearance and evolution of the radiative and nonradiative polariton branches are traced as the length varies from two monomers to limiting values, above which the spectrum no longer undergoes significant changes. The dependences of the frequencies and radiative widths on the polariton wave vector are found for various orientations of the dipole moment of the quantum transition. The evolution of superradiance as the length of the crystal increases is traced. Some previously unknown significant features of the polariton spectrum are noted particularly the damping of the branch traditionally termed nonradiative as a consequence of emission from the end faces.

Radiative and non-radiative polariton structure of superlattices

Optical properties of multilayered materials, including synthesized superlattices received special attention in the last few years. To some extent, reflectance and absorption of these materials are adjustable: the polariton structure depends sensitively on the layer geometry.Though the approach considered here is applicable to any stratified structure, we emphasize on polaritons of semi-infinite superlattices, that is superlattices which exhibit a free surface. In these thin-film structures, the accumulation of interfaces gives rise to peculiar electromagnetic eigenmodes, distributed as continuous frequency bands. The termination of the superlattice at the surface modifies the density of these modes, as compared with the mode density of an infinite, truly periodic superlattice. In particular, one notices the appearance of isolated branches analogous to surface polariton modes of semi-infinite homogeneous materials.We approach the description of radiative and non-radiative modes, including finite life-time effects, from the point of view of scattering theory, using a Green's function technique. The local density of states of the polariton modes is calculated and provides a complete information on allowed electromagnetic excitations, as a function of wavelength, at any depth in the superlattice. These results will be used to discuss reflectance and attenuated total reflection experiments on superlattices.

Surface polaritons on molecular crystals: An experimental study of anthracene

We report studies of surface polaritons on the (ab) face of crystalline anthracene by the method of attenuated total reflection. We find that: (a) At low temperature (less than 100 °K) a surface polariton propagating down the b axis on the (ab) face is a well defined excitation. The estimated dephasing time at 16 °K is 0.1 psec, and the surface polariton can move coherently along the surface for up to 2 μm. (b) At higher temperatures the surface polariton is not a well defined excitation by virtue of scattering by lattice phonons. (c) The single particle 391 cm−1 vibronic dipolar surface polariton is also a well defined mode at low temperature. (d) The two particle scattering resonance arising from the 391 cm−1 vibration is seen in both the region of nonradiative modes and the region of radiative modes. (e) Three types of nonradiative polariton mode are observed below the exciton origin in thin crystals. Each of these is characterized by a different form of dispersion relation.