Photonic Bilayer Chern Insulator with Corner States

Area of Science:

• Condensed Matter Physics
• Photonics
• Topological Materials

Background:

• Photonic Chern insulators, based on gyromagnetic photonic crystals with broken time-reversal (TR) symmetry, feature gapless chiral edge states (CESs) for unidirectional propagation.
• Stacking Chern insulators with opposite Chern numbers theoretically closes CESs, leading to a topological phase transition, but experimental realization is lacking.

Purpose of the Study:

• To experimentally investigate the topological phase transition in a bilayer gyromagnetic photonic crystal with an antiferromagnetic layer configuration.
• To explore the emergence of novel topological states and their properties under interlayer coupling.

Main Methods:

• Fabrication and experimental observation of a bilayer gyromagnetic photonic crystal.
• Analysis of the effects of interlayer coupling on the electronic band structure and edge states.
• Characterization of emergent corner states and their resilience to defects.

Main Results:

• Experimental evidence of a topological phase transition from a Chern insulating phase to a higher-order topological phase induced by interlayer coupling.
• Observation of the gapping of chiral edge states (CESs) and the emergence of robust corner states within the band gap.
• Identification of corner modes as Jackiw-Rebbi-type topological domain wall modes, stable without local symmetries.

Conclusions:

• The study experimentally validates the theoretical prediction of achieving higher-order topological phases in gyromagnetic photonic crystals.
• The observed corner states exhibit enhanced resilience to defects, offering potential for robust topological devices.
• This work provides a new platform for exploring higher-order topology in photonic systems.