  Topological mechanical metamaterials translate condensed matter phenomena,
like non-reciprocity and robustness to defects, into classical platforms. At
small scales, topological nanoelectromechanical metamaterials (NEMM) can enable
the realization of on-chip acoustic components, like unidirectional waveguides
and compact delay-lines for mobile devices. Here, we report the experimental
realization of NEMM phononic topological insulators, consisting of
two-dimensional arrays of free-standing silicon nitride (SiN) nanomembranes
that operate at high frequencies (10-20 MHz). We experimentally demonstrate the
presence of edge states, by characterizing their localization and Dirac
cone-like frequency dispersion. Our topological waveguides also exhibit
robustness to waveguide distortions and pseudospin-dependent transport. The
suggested devices open wide opportunities to develop functional acoustic
systems for high-frequency signal processing applications.
