2023/06/05 by Tianyuan Liu, Wei Yan, Liu, Tianyuan +3
Engineering · Physics and Astronomy · #FOS: Physical sciences #Mesoscale and Nanoscale Physics (cond-mat.mes-hall) #Optics (physics.optics) #Photorefractive and Nonlinear Optics #Quantum optics and atomic interactions #Terahertz technology and applications
paper · pdf · doi:10.48550/arxiv.2306.02633
openalex publication_date 2023/06/05 · openalex created_date 2023/06/07 · openalex updated_date 2026/07/28
Breaking parity (P) symmetry in C6 symmetric crystals is a common routine to implement a valley-topological phase. At an interface between two crystals of opposite valley phases, the so-called valley topological edge states emerge, and they have been proven useful for wave transport with robustness against 120^∘ bending and a certain level of disorder. However, whether these attractive transport features are bound with the valley topology or due to topological-irrelevant mechanisms remains unclear. In this letter, we discuss this question by examining transport properties of photonic edge states with varied degrees of the P-breaking that tune the valley topology, and reveal that the edge states preserve their transport robustness insensitive to the topology even when the P-symmetry is recovered. Instead, a unique modal character of the edge states -- with localized momentum hotspots around high-symmetric K (K') points -- is recognized to play the key role, which only concerns the existence of the valleys in the bulk band structures, and has no special requirement on the topology. The "non-topological" notion of valley edge states is introduced to conceptualize this modal character, leading to a coherent understanding of bending immunity in a range of edge modes implemented in C3 symmetric crystals -- such as valley topological edge states, topological edge states of 2D Zak phase, topological-trivial edge states and so on, and to new designs in general rhombic lattices -- with exemplified bending angle as large as 150^∘.