  In the last years there have been multiple proposals in nanophotonics to
mimic topological condensed matter systems. However, nanoparticles have degrees
of freedom that atoms lack of, like dimensions or shape, which can be exploited
to explore topology beyond electronics. Elongated nanoparticles can act like
projectors of the electric field in the direction of the major axis. Then, by
orienting them in an array the coupling between them can be tuned, allowing to
open a gap in an otherwise gapless system. As a proof of the potential of the
use of orientation of nanoparticles for topology, we study 1D chains of prolate
spheroidal silver nanoparticles. We show that in these arrays spatial
modulation of the polarization allows to open gaps, engineer hidden crystalline
symmetries and to switch on/off or left/right edge states depending on the
polarization of the incident electric field. This opens a path towards
exploiting features of nanoparticles for topology to go beyond analogues of
condensed matter systems.
