M. D. Coutinho-Filho

Delocalization and spin-wave dynamics in ferromagnetic chains with long-range correlated random exchange

We study the one-dimensional quantum Heisenberg ferromagnet with exchange couplings exhibiting long-range correlated disorder with power spectrum proportional to 1/k α , where k is the wave vector of the modulations on therandom coupling landscape. By using the renormalization group, integration of the equations of motion, and exact diagonalization, we compute the spin-wave localization length and the mean-square displacement of the wave packet. We find that, associated with the emergence of extended spin waves in the low-energy region for α>1, the wave-packet mean-square displacement changes from a long-time super diffusive behavior for a 1. At the vicinity of α=1, the mobility edge separating the extended and localized phases is shown to scale with the degree of correlation as E c (α-1) 1 / 3 .

Delocalization in harmonic chains with long-range correlated random masses

We study the nature of collective excitations in harmonic chains with masses exhibiting long-range correlated disorder with a power spectrum proportional to

Critical behavior of the two-dimensional Anderson model with long-range correlated disorder

{1/k}^{\ensuremath{\alpha}},

Frustration-induced quantum phase transitions in a quasi-one-dimensional ferrimagnet: Hard-core boson map and the Tonks-Girardeau limit

where k is the wave vector of the modulations on the random masses landscape. Using a transfer-matrix method and exact diagonalization, we compute the localization length and participation ratio of eigenmodes within the band of allowed energies. We find extended vibrational modes in the low-energy region for

From dilute to dense self-avoiding walks on hypercubic lattices

\ensuremath{\alpha}g1.

Lattice covering time in D dimensions: theory and mean field approximation

In order to study the time evolution of an initially localized energy input, we calculate the second moment

FMR studies in the ferromagnetic semiconductors CdCr2Se4 and HgCr2Se4

{M}_{2}(t)

Lifshitz points and Landau theory in the presence of a magnetic field

of the energy spatial distribution. We show that

Scaling close to a Mott transition in an exactly soluble model

{M}_{2}(t),

Monte Carlo studies of the spin-glass-like phase in Fe0.25Zn0.75F2

besides being dependent of the specific initial excitation and exhibiting an anomalous diffusion for weakly correlated disorder, assumes a ballistic spread in the regime