  Recently, the concept of valley pseudospin, labeling quantum states of energy
extrema in momentum space, has attracted enormous attention because of its
potential as a new type of information carrier. Here, we present surface
acoustic wave (SAW) waveguides, which utilize and transport valley pseudospins
in two-dimensional SAW phononic crystals (PnCs). In addition to a direct
visualization of the valley-dependent states excited from the corresponding
chiral sources, the backscattering suppression of SAW valley-dependent edge
states transport is observed in sharply curved interfaces. By means of band
structure engineering, elastic wave energy in the SAW waveguides can be
transported with remarkable robustness, which is very promising for new
generations of integrated solid-state phononic circuits with great versatility.
