Phonon manipulation with valley-Hall junctions

Abstract

In this work, we investigate experimentally the existence of in-plane valley Hall edge states in hexagonal lattices with relaxed space inversion symmetry and we exploit them to realize non-trivial backscattering-free interfaces. We propose special tessellations of lattice domains in which multiple non-trivial domain walls coalesce to form junctions, and we study how guided waves behave when they impinge on such junctions. We show that, through a proper selection of the interface types and orientations, it is possible to achieve junctions with different and exotic wave manipulation capabilities. Specifically, we discuss two applications. The first is a direction-selective splitter, which endows its host lattice with asymmetric wave transport characteristics. The second is a signal delayer that is realized by embedding in the lattice a non-trivial waveguide loop, along which the energy can be temporarily trapped and periodically released. These junctions can serve as building blocks for a new structural logic paradigm enabled by topological mechanics.