D.H.A.L. Anselmo

Octonacci photonic quasicrystals

Abstract We study theoretically the transmission spectra in one-dimensional photonic quasicrystals, made up of SiO2(A) and TiO2(B) materials, organized following the Octonacci sequence, where the nth-stage of the multilayer S n is given by the rule S n = S n - 1 S n - 2 S n - 1 , for n ⩾ 3 and with S 1 = A and S 2 = B . The expression for transmittance was obtained by employing a theoretical calculation based on the transfer-matrix method. For normally incident waves, we observe that, for a same generation, the transmission spectra for transverse electric (TE) and transverse magnetic (TM) waves are equal, at least qualitatively, and they present a scaling property where a self-similar behavior is obtained, as an evidence that these spectra are fractals. The spectra show regions where the omnidirectional band gaps emerges for specific generations of Octonacci photonic structure, except to TM waves. For TE waves, we note that all of them have almost the same width, for different generations. We also report the localization of modes as a consequence of the quasiperiodicity of the heterostructure.

Non-linear spin-wave spectra in anisotropic magnetic superlattices

Abstract We present a theory for the dispersion relation and non-linear processes of spin-waves in a superlattice made up of two Heisenberg ferromagnets. Our calculations are carried out for the exchange-dominated regime, stressing the contribution of the surface modes. We consider the ferromagnetic materials described by a Heisenberg Hamiltonian, with the inclusion of both the uniaxial and non-uniaxial components of the single-ion anisotropy. Our theoretical model is based on the Holstein–Primakoff transformation to boson operators, while a Green function formalism with Feynman diagrams is employed as a perturbation theory to calculate the non-linear processes.