Extended spin waves in aperiodic ferromagnetic chains
Instituto de Física, Universidade Federal de Alagoas, Maceió AL, 57072-970, Brazil
Corresponding author: a email@example.com
Revised: 7 August 2007
Published online: 22 September 2007
In this work, a one-dimensional quantum Heisenberg ferromagnet with aperiodic exchange couplings is considered. To produce an aperiodic distribution of exchange couplings, it is used a sinusoidal function whose phase φ varies as a power-law, φ∝nν, where n labels the positions along the chain. By using exact diagonalization, the spin-wave participation number and the local density of states are computed. The numerical calculations indicate that for 0 < ν < 1, this ferromagnetic system displays a phase of extended spin waves in the low-energy region. For ν > 1 all spin waves are localized except for the zero energy mode. By integrating the time-dependent Schrödinger equation, the temporal evolution of the mean-square displacement of the wave-packet was followed. Associated with the emergence of extended spin waves, it was observed that the wave-packet mean-square displacement displays a ballistic spread.
PACS: 75.30.Ds – Spin waves / 73.23.Ad – Ballistic transport / 73.20.Jc – Delocalization processes / 72.15.Rn – Localization effects (Anderson or weak localization)
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2007