Rolling Waves with Non-Paraxial Phonon Spins

TL;DR

This paper introduces a new class of elastic waves called rolling waves with non-paraxial phonon spins, achieved in anisotropic media, with potential applications in spin-based acoustic and mechanical technologies.

Contribution

It defines non-paraxial phonon spins, derives conditions for their existence in anisotropic media, and designs architected materials to support these novel waves.

Findings

Demonstration of rolling waves with non-parallel spin and wave vector

Design of anisotropic structures supporting rolling waves

Numerical validation of spin manipulation via reflection

Abstract

We demonstrate a new class of elastic waves in the bulk: When longitudinal and transverse components propagate at the same speed, rolling waves with a spin that is not parallel to the wave vector can emerge. First, we give a general definition of spin for traveling waves. Then, since rolling waves cannot exist in isotropic solids, we derive conditions for anisotropic media and proceed to design architected materials capable of hosting rolling waves. Numerically, we show spin manipulations by reflection. Structures reported in this work can be fabricated using available techniques, opening new possibilities for spin technologies in acoustics, mechanics and phononics.