Topological Protection in Densely Packed Anisotropic Colloids*

It has been long known that there exist topologically protected phases in strongly coupled
systems dominated by quantum effects. Recently, analogous phases have been discovered in
classical systems of mechanical metamaterials. Here, we demonstrate the existence of
topologically protected phases in systems of densely-packed, hard, anisotropic colloids.
Previously reported transitions in dense packings as a function of the constituent particle shape
lead to the existence of topologically protected thermodynamic phases in such systems, which
are shown to be stable away from the limit of densest packing, down to packing fractions of
about 75%. Our discovery expands the library of topological phases, and realizing these phases
in experiment could provide a new means of producing complex soft materials that are
resistant to thermal fluctuations, with applications in robust information storage and
processing, and plasmonic materials.