  The interplay between real-space topological lattice defects and the
reciprocal-space topology of energy bands can give rise to various novel
phenomena, such as one-dimensional topological helical modes bound to screw
dislocations in three-dimensional topological insulators. Here, we present a
direct experimental observation of this intriguing phenomenon using an acoustic
analog of a weak three-dimensional topological insulator. The existence of
topological helical modes bound to the dislocation is verified experimentally
through spin-resolved field mapping, and numerically through tight-binding and
finite-element calculations. The one-dimensional helical channels can serve as
robust waveguides in three-dimensional settings. This experiment paves the way
to studying the novel physical modes and functionalities enabled by topological
lattice defects in three-dimensional classical topological materials.
