Tunable Insulator-Metal Transitions and Flat Bands in Domain-Wall-Engineered Monolayer In₂Se₃

Ferroelectric domain walls (DWs) provide a promising platform for dynamically tuning electronic properties at the nanoscale. Using first-principles calculations, we demonstrate that charged DWs in monolayer α-In₂Se₃ enable versatile band engineering across one and two dimensions. In one-dimensional DW arrays, the separation between tail-to-tail and head-to-head DWs controls the band gap: with increasing inter-wall distance, the valence and conduction bands, dominated respectively by the oppositely charged DWs, shift in opposite directions under contrasting local electrostatic potentials, leading to continuous gap reduction and ultimately an insulator-to-metal transition. Extending to two dimensions, periodic DW networks form a breathing Kagome lattice, wherein each DW segment acts as a “super-atom”, yielding nearly dispersionless flat bands near the Fermi level. In addition, an isolated conduction band originating from the P↓ domains emerges near the Fermi level with decreasing bandwidth as the superlattice size increases, giving rise to an effective triangular lattice. Our findings establish DW-engineered In₂Se₃ as a reconfigurable platform that bridges ferroelectric switching with quantum materials design, offering a promising route toward a possible platform for exploring emergent quantum phenomena in artificially engineered lattices.