Phononic topological states in 1D quasicrystals.

In this work, we address the study of phonons propagating on a one-dimensional quasiperiodic lattice, where the atoms are considered bounded by springs whose strength are modulated by equivalent Aubry-André hoppings. As an example, from the equations of motion, we obtained the equivalent phonon spectrum of the well known Hofstadter butterfly. We have also obtained extended, critical, and localized regimes in this spectrum. By introducing the equivalent Aubry-André model through the variation of the initial phase [Formula: see text], we have shown that border states for phonons are allowed to exist. These states can be classified as topologically protected states (topological states). By calculating the inverse participation rate, we describe the localization of phonons and verify a phase transition, characterized by the critical value of [Formula: see text], where the states of the system change from extended to localized, precisely like in a metal-insulator phase transition.