The Aubry-Andr\'e-Harper model provides a paradigmatic example of aperiodic order in a one-dimensional lattice displaying a delocalization-localization
phase transition at a finite critical value $V_c$ of the quasiperiodic potential amplitude $V$.
In terms of dynamical behavior of the system, the phase transition is
discontinuous when one measures the quantum diffusion exponent $\delta$ of wave packet spreading, with $\delta=1$ in the delocalized phase $V