Controllable flatbands via non-Hermiticity

We propose a flexible way to design and control flatbands in photonic systems with balanced gain and loss. We investigate a lattice model constructed from two parity-time (PT)-symmetric dimer systems, which give rise to two flatbands. By tuning the non-Hermiticity in this composite lattice, the flatbands can be manipulated into the regime of the dispersive bands and remain completely flat, which is protected by the PT symmetry. When reaching the exceptional point (EP), where two flatbands merge into one flatband, and surpassing the EP, one of the flatbands transforms into a partial flatband, while the imaginary parts of the band structure also appear in the form of multiple flatbands. We also discover that dimensionality plays an important role in controlling flatbands in a non-Hermitian manner. Our results could be potentially important for manipulating the dynamics and localization of light in non-Hermitian open systems. © 2023 Author(s).