On Transport Properties of Isotropic Quasiperiodic XY Spin Chains

We consider isotropic XY spin chains whose magnetic potentials are quasiperiodic and the effective one-particle Hamiltonians have absolutely continuous spectra. For a wide class of such XY spin chains, we obtain lower bounds on their Lieb-Robinson velocities b in terms of group velocities of their effective Hamiltonians: b >= ess sup([0,1]) 2/pi dE/dN. where E is considered as a function of the integrated density of states.