Imaging valley-vortex edge modes in a phononic crystal at ultrahigh frequencies

We perform optical measurements and numerical simulations of guided phonon propagation in novel topological phononic crystal structures at ultrahigh frequencies. The structures support valley-polarized states that exhibit an energy vortex nature and propagate with high efficiency at domain boundaries because backscattering is suppressed due to conservation of time reversal symmetry. We extract frequency- and time-resolved spatial mode patterns and k-space images, together with dispersion relations. We investigate the conditions required for robust propagation along interfaces and thereby observe very high efficiency waveguiding.