1,721,281 research outputs found
PHASE-TRANSITION IN THE MULTIFRACTAL SPECTRUM OF THE THUE-MORSE LATTICE
No full textA study of the scaling properties of the electron energy spectrum for a one-dimensional tight-binding model with Thue-Morse on-site potential is presented. This system is interesting because it is not periodic, quasiperiodic or random. The multifractal scaling functions f(α) and τ(q) have been numerically calculated using periodic approximations of the spectrum. In the thermodynamic limit, it appears that τ(q) = q − 1 for q 1; correspondingly, the f(α) curve reduces to the two points (α=1, f=1) and (α=1, f=0). This behavior is not sensitive to the strenght of the Thue-Morse potential in the range investigated and it is quite different from the behavior exhibited by quasiperiodic systems. The present results suggest that the spectrum of the Thue-Morse lattice contains absolutely continuous parts (band-like extended states) plus pure point singularities (atomic-like localized states)
Optical nonlinearities in organic-inorganic nanostructures
No full textRapid advances in the growth techniques of multilayer structures incorporating molecular as well as covalent crystals allow room for designing novel systems with great flexibility. We have recently considered the hybrid combination consisting of an organic and an inorganic quantum well in which the fundamental electronic excitations have a mixed character of Frenkel and Wannier excitons. In such a structure, the properties of both molecular and covalent crystals conspire to overcome the basic limitations of the individual constituents and a greatly enhanced nonlinear optical response can be achieved. Beside a discussion of the theoretical model, we present here the calculated spectra of the hybrid exciton polariton resonances for specific experimental configurations: attenuated total reflection in the nonradiative regime and normal incidence transmission and absorption in the radiative regime
DETERMINISTIC NONPERIODIC STRUCTURES
No full textAperiodic structures which are perfectly ordered, but lack translational symmetry, can be considered as intermediate between crystalline and amorphous systems. Their wave-functions and spectra exhibit unusual properties. A one-dimensional model, known as the Thue-Morse lattice, is here investigated; it is particularly interesting because ft is deterministic non-periodic, but not quasi-periodic. The propagation of both electrons and photons is considered and the corresponding spectra are characterized with a multifractal analysis. The multifractal scaling function tau(q) tends in both cases to a non-analytic limit that implies the presence of both extended and exponentially localized states, as confirmed by the behaviour of the wave functions
ANISOTROPIC-C60-C60 INTERMOLECULAR POTENTIAL
No full textThe intermolecular potential for solid fullerene is calculated within the Gordon-Kim statistical approach. The isotropic part of the potential agrees semi-quantitatively with experimental data. For the orientationally ordered Pa3BAR phase, two energy minima are predicted at setting angles of 23-degrees and 87-degrees, close to those experimentally found. The electrostatic interaction is shown to be significantly affected by overlap effects at intermolecular separations typical of the solid phases
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