Frenkel Excitons in Random Systems With Correlated Gaussian Disorder

Optical absorption spectra of Frenkel excitons in random one-dimensional systems are presented. Two models of inhomogeneous broadening, arising from a Gaussian distribution of on-site energies, are considered. In one case the on-site energies are uncorrelated variables whereas in the second model the on-site energies are pairwise correlated (dimers). We observe a red shift and a broadening of the absorption line on increasing the width of the Gaussian distribution. In the two cases we find that the shift is the same, within our numerical accuracy, whereas the broadening is larger when dimers are introduced. The increase of the width of the Gaussian distribution leads to larger differences between uncorrelated and correlated disordered models. We suggest that this higher broadening is due to stronger scattering effects from dimers.Comment: 9 pages, REVTeX 3.0, 3 ps figures. To appear in Physical Review

Nonequilibrium critical dynamics of the three-dimensional gauge glass

We study the non-equilibrium aging behavior of the gauge glass model in three dimensions at the critical temperature. We perform Monte Carlo simulations with a Metropolis update, and correlation and response functions are calculated for different waiting times. We obtain a multiplicative aging scaling of the correlation and response functions, calculating the aging exponent $b$ and the nonequilibrium autocorrelation decay exponent $\lambda_c/z_c$. We also analyze the fluctuation-dissipation relationship at the critical temperature, obtaining the critical fluctuation-dissipation ratio $X_\infty$. By comparing our results with the aging scaling reported previously for a model of interacting flux lines in the vortex glass regime, we found that the exponents for both models are very different.Comment: 7 pages, 4 figures. Manuscript accpeted for publication in PR

FIBONACCI SUPERLATTICES OF NARROW-GAP III-V SEMICONDUCTORS

We report theoretical electronic structure of Fibonacci superlattices of narrow-gap III-V semiconductors. Electron dynamics is accurately described within the envelope-function approximation in a two-band model. Quasiperiodicity is introduced by considering two different III-V semiconductor layers and arranging them according to the Fibonacci series along the growth direction. The resulting energy spectrum is then found by solving exactly the corresponding effective-mass (Dirac-like) wave equation using tranfer-matrix techniques. We find that a self-similar electronic spectrum can be seen in the band structure. Electronic transport properties of samples are also studied and related to the degree of spatial localization of electronic envelope-functions via Landauer resistance and Lyapunov coefficient. As a working example, we consider type II InAs/GaSb superlattices and discuss in detail our results in this system.Comment: REVTeX 3.0, 16 pages, 8 figures available upon request. To appear in Semiconductor Science and Technolog

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 can be then used to determine experimentally the ordering of traps.Comment: REVTeX 3.0 + 3PostScript Figures + epsf.sty (uuencoded). To appear in Physical Review