Negative Refraction and Partition in Acoustic Valley Materials of a Square Lattice

Acoustic valley materials, usually constructed in a hexagonal lattice, provide an additional degree of freedom (so-called valleys in their band structures) for manipulating sound waves. This study realizes such a material in a $s\phantom{\rule{0}{0ex}}q\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}e$ lattice, in which the topological transport and negative refraction of acoustic kink waves are observed in experiment. At the intersection of channels, a counterintuitive transport phenomenon is seen: The kink waves tend to choose the path that contains a sharp turn. These findings may be useful for directional vocalization, noise reduction, and beam splitting.