Optical absorption in Fibonacci lattices at finite temperature

We consider the dynamics of Frenkel excitons on quasiperiodic lattices, focusing our attention on the Fibonacci case as a typical example. We evaluate the absorption spectrum by solving numerically the equation of motion of the Frenkel-exciton problem on the lattice. Besides the main absorption line, satellite lines appear in the high-energy side of the spectra, which we have related to the underlying quasiperiodic order. The influence of lattice vibrations on the absorption line shape is also considered. We find that the characteristic features of the absorption spectra should be observable even at room temperature. Consequently, we propose that excitons act as a probe of the topology of the lattice even when thermal vibrations reduce their quantum coherence

Lump solitons in a higher-order nonlinear equation in 2 + 1 dimensions

We propose and examine an integrable system of nonlinear equations that generalizes the nonlinear Schr ̈ odinger equation to 2 + 1 dimensions. This integrable system of equations is a promising starting point to elaborate more accurate models in nonlinear optics and molecular systems within the continuum limit. The Lax pair for the system is derived after applying the singular manifold method. We also present an iterative procedure to construct the solutions from a seed solution. Solutions with one-, two-, and three-lump solitons are thoroughly discussed

Stark ladders in periodically si-delta-doped gaas

We study theoretically the electronic structure of periodically Si delta-doped GaAs subject to a homogeneous electric field applied along the growth direction. The space-charge potential due to delta doping is obtained by means of the Thomas-Fermi approach. Analyzing the change in the density of states in the superlattice introduced in the electric field, we observe a set of equally-spaced sharp peaks corresponding to Stark-ladder resonances. Intrinsic broadening of resonances turns out to be smaller than the level spacing in the whole range of the electric field we consider. We use the inverse participation ratio to evaluate the spatial extent of electron wave functions, and we find that the Stark-ladder spectrum is related to a strong-localization regime at high field

Fluorescence decay in aperiodic Frenkel lattices

We study motion and capture of excitons in self-similar linear systems in which interstitial traps are arranged according to an aperiodic sequence, focusing our attention on Fibonacci and Thue-Morse systems as canonical examples. The decay of the fluorescence intensity following a broadband pulse excitation is evaluated by solving the microscopic equations of motion of the Frenkel exciton problem. We find that the average decay is exponential and depends only on the concentration of traps and the trapping rate. In addition, we observe small-amplitude oscillations coming from the coupling between the low-lying mode and a few high-lying modes through the topology of the lattice. These oscillations are characteristic of each particular arrangement of traps and they are directly related to the Fourier transform of the underlying lattice. Our predictions then can be used to determine experimentally the ordering of traps

Physical nature of critical wave functions in Fibonacci systems-Errata (vol 76, pg 2957, 1996)

© 1997 The American Physical Society.Depto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu

Scanning electron acoustic microscopy observations of twins and grain boundaries in III‐V materials

Polycrystalline GaP and InP have been observed by scanning electron acoustic microscopy. While grain boundaries show a weak contrast, twinned regions are clearly revealed. Results suggest that the contrast observed is related to signal generation by a piezoelectric‐coupling mechanis

Erratum: Suppression of localization in kronig-penney models with correlated disorder (Vol. 49, PG 147, 1994)

We consider the electron dynamics and transport properties of one-dimensional continuous models with random, short-range correlated impurities. We develop a generalized Poincare map formalism to cast the Schrodinger equation for any potential into a discrete set of equations, illustrating its application by means of a specific example. We then concentrate on the case of a Kronig-Penney model with dimer impurities. The previous technique allows us to show that this model presents infinitely many resonances (zeroes of the reflection coefficient at a single dimer) that give rise to a band of extended states, in contradiction with the general viewpoint that all one-dimensional models with random potentials support only localized states. We report on exact transfer-matrix numerical calculations of the transmission coefFicient, density of states, and localization length for various strengths of disorder. The most important conclusion so obtained is that this kind of system has a very large number of extended states. Multifractal analysis of very long systems clearly demonstrates the extended character of such states in the thermodynamic limit. In closing, we brieBy discuss the relevance of these results in several physical contexts

Electron scattering on disordered double-barrier GaAs-AlxGa1-xAs heterostructures

We present a novel model to calculate vertical transport properties such as conductance and current in unintentionally disordered double-barrier GaAs-AlxGa1-xAs heterostructures. The source of disorder comes from interface roughness at the heterojunctions (lateral disorder) as well as spatial inhomogeneities of the Al mole fraction in the barriers (compositional disorder). Both lateral and compositional disorder break translational symmetry along the lateral direction and therefore electrons can be scattered off the growth direction. The model correctly describes channel mixing due to these elastic scattering events. In particular, for realistic degree of disorder, we have found that the effects of compositional disorder on transport properties are negligible as compared to the effects due to lateral disorder