Boundary deconfined quantum criticality at transitions between symmetry-protected topological chains

Understand

Decades of research have revealed a deep understanding of topological quantum matter with protected edge modes.

• We report that even richer physics emerges when tuning between two topological phases of matter whose respective edge modes are incompatible.
• The frustration at the edge leads to novel boundary physics, such as symmetry-breaking phases with exotic non-Landau transitions -- even when the edge is zero-dimensional.
• As a minimal case study we consider spin chains with $\mathbb{Z}_3 \times \mathbb{Z}_3$ symmetry, exhibiting two nontrivial symmetry-protected topological (SPT) phases.