Trivial topology-entailed states at interfaces between identical topological phases

Abstract

Topological edge states arise at boundaries between bulk phases with distinct topological invariants and are characterized by robust, often chiral transport. When two domains sharing identical bulk topology are brought into contact, their counterpropagating edge modes are generally expected to hybridize and cancel each other out in the process. Here, we show that this cancellation can be lifted by trivial parameter variations at the interface, giving rise to a distinct class of gap-localized inter-face modes, which we term trivial topology-entailed (TTE) states. Using anomalous Floquet photonic lattices as a concrete platform, we experimentally observe the formation of bidirectional TTE states between topologically equivalent domains. In particular, we demonstrate their spectral confinement within bulk gaps, their coherent coupling to conventional chiral edge channels, and their ability to mediate interface-guided transport across composite lattices. Our results establish TTE states as a general interface phenomenon in composite topological systems and provide a unified framework for understanding hybridized boundary modes beyond conventional bulk-boundary correspondence.