  The bulk-boundary correspondence, which links a bulk topological property of
a material to the existence of robust boundary states, is a hallmark of
topological insulators. However, in crystalline topological materials the
presence of boundary states in the insulating gap is not always necessary since
they can be hidden in the bulk energy bands, obscured by boundary artifacts of
non-topological origin, or, in the case of higher-order topology, they can be
gapped altogether. Crucially, in such systems the interplay between
symmetry-protected topology and the corresponding symmetry defects can provide
a variety of bulk probes to reveal their topological nature. For example, bulk
crystallographic defects, such as disclinations and dislocations, have been
shown to bind fractional charges and/or robust localized bound states in
insulators protected by crystalline symmetries. Recently, exotic defects of
translation symmetry called partial dislocations have been proposed as a probe
of higher-order topology. However, it is a herculean task to have experimental
control over the generation and probing of isolated defects in solid-state
systems; hence their use as a bulk probe of topology faces many challenges.
Instead, here we show that partial dislocation probes of higher-order topology
are ideally suited to the context of engineered materials. Indeed, we present
the first observations of partial-dislocation-induced topological modes in 2D
and 3D higher-order topological insulators built from circuit-based resonator
arrays. While rotational defects (disclinations) have previously been shown to
indicate higher-order topology, our work provides the first experimental
evidence that exotic translation defects (partial dislocations) are bulk
topological probes.
