arXiv subjects

F. A. B. F. de Moura

Publications and source records attributed to F. A. B. F. de Moura.

20 records · Page 2Linked to original sources

arXiv2002

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 the random coupling landscape. By using 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 $α<1$ to a long-time ballistic behavior for $α> 1$. 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 $E_c\propto (α-1)^{1/3}$.

cond-mat.stat-mech↗

arXiv2000

Convergence of the critical attractor of dissipative maps: Log-periodic oscillations, fractality and nonextensivity

For a family of logistic-like maps, we investigate the rate of convergence to the critical attractor when an ensemble of initial conditions is uniformly spread over the entire phase space. We found that the phase space volume occupied by the ensemble W(t) depicts a power-law decay with log-periodic oscillations reflecting the multifractal character of the critical attractor. We explore the parametric dependence of the power-law exponent and the amplitude of the log-periodic oscillations with the attractor's fractal dimension governed by the inflexion of the map near its extremal point. Further, we investigate the temporal evolution of W(t) for the circle map whose critical attractor is dense. In this case, we found W(t) to exhibit a rich pattern with a slow logarithmic decay of the lower bounds. These results are discussed in the context of nonextensive Tsallis entropies.

cond-mat.stat-mech↗