Soft Materials Seminar - "Topological phononic valley Hall effect in self-assembled nanoparticle superlattices"

Lattice engineering in atomic systems has enabled diverse topological states, while self-assembled nanoparticle superlattices offer a scalable route to nanoscale materials with tailored properties. Here, we bridge these fields by demonstrating the topological valley Hall effect in a corrugated honeycomb lattice self-assembled from gold tetrahedral nanoparticles. Liquid-phase transmission electron microscopy, through a phonon mode nanoscopy workflow, directly resolves its three defining features: a gapped Dirac cone, valley-contrasting Berry curvature, and a valley Chern number of ±½.  Simulations reproduce these features and reveal the roles of stiffness anisotropy and substrate-assisted symmetry breaking. We further observe a topological interface mode at domain walls, establishing nanoparticle self-assembly as a bottom-up platform for topological engineering.