Realization of broadband ultrasonic chiral Landau levels in an elastic metamaterial

Metamaterials with Landau levels induced by synthetic pseudomagnetic fields present an exciting avenue for manipulating elastic waves. Traditionally, these Landau levels in elastic metamaterials are generated by out-of-plane pseudomagnetic fields, resulting in flat-band dispersions with limited bandwidth. In this study, we develop an elastic metamaterial with broadband ultrasonic chiral Landau levels induced by in-plane pseudomagnetic fields, which are synthesized by introducing linearly increased effective Dirac mass via locally breaking the inversion symmetry of each unit cell. We experimentally observe broadband zeroth-order chiral Landau levels for ultrasonic energy transmission. Additionally, we report the experimental observation of snake states, arising from the interaction between zeroth-order and first-order Landau levels. The excellent robustness of the chiral Landau levels is also experimentally validated. Our work suggests a way for realizing broadband ultrasonic chiral Landau levels in elastic systems, with promising potential for applications in engineering devices for integrated communication of elastic waves.