Emergent topological interfacial states in 3D photonic crystals via half-period structural shifts

Area of Science:

• Photonics
• Condensed Matter Physics
• Materials Science

Background:

• Higher-order two-dimensional (2D) topological photonic crystals are well-studied.
• Three-dimensional (3D) analogues are scarce, limiting exploration of richer topological phenomena and robust 3D photonic networks.

Purpose of the Study:

• To propose and demonstrate a strategy for engineering 3D topological photonic crystals.
• To generalize the Su-Schrieffer-Heeger model's topological interfaces to three dimensions.

Main Methods:

• Designing a hexagonal lattice photonic crystal with tunable band gaps.
• Constructing interfaces between inversion-symmetric lattices and their half-lattice-shifted counterparts.
• Performing numerical simulations to verify topological properties and state emergence.

Main Results:

• Demonstrated non-trivial Zak phase (π) along all three primitive lattice directions in both original and half-period-shifted configurations.
• Observed emergence of surface states at planar interfaces.
• Identified hinge states at 1D corners and 0D corner states, confirming higher-order topology.

Conclusions:

• The proposed interface strategy successfully engineers 3D topological photonic crystals.
• This work advances the design principles for 3D topological materials.
• Opens new possibilities for fault-tolerant photonic circuits and multidimensional light trapping.