  Common wisdom believes that the Pancharatnam-Berry (PB) geometric phase is
absent in acoustics due to the spin-0 nature of sound waves. We theoretically
and experimentally demonstrate that the PB phase can emerge in surface sound
waves (SSWs) carrying transverse spin. The phase differs for the SSWs
propagating in opposite directions due to spin-momentum locking. We further
realize acoustic PB metasurfaces for nearly arbitrary wavefront manipulation.
Our work provides the missing piece of acoustic geometric phases, offering new
insights into the fundamental properties of sound waves and opening a new
avenue for sound manipulation based on the PB phase.
