Emergence of metal–semiconductor phase transition in MX₂ (M = Ni, Pd, Pt; X = S, Se, Te) moiré superlattices

Two-dimensional (2D) moiré superlattices with a small twist in orientation exhibit a broad range of physical properties due to the complicated intralayer and interlayer interactions modulated by the twist angle. Here, we report a metal–semiconductor phase transition in homojunction moiré superlattices of NiS₂ and PtTe₂ with large twist angles based on high-throughput screening of 2D materials MX₂ (M = Ni, Pd, Pt; X = S, Se, Te) via density functional theory (DFT) calculations. Firstly, the calculations for different stacking configurations (AA, AB and AC) reveal that AA stacking ones are stable for all the bilayer MX₂. The metallic or semiconducting properties of these 2D materials remain invariable for different stacking without twisting except for NiS₂ and PtTe₂. For the twisted configurations, NiS₂ transfers from metal to semiconductor when the twist angles are 21.79°, 27.79°, 32.20° and 60°. PtTe₂ exhibits a similar transition at 60°. The phase transition is due to the weakened d–p orbital hybridization around the Fermi level as the interlayer distance increases in the twisted configurations. Further calculations of untwisted bilayers with increasing interlayer distance demonstrate that all the materials undergo metal–semiconductor phase transition with the increased interlayer distance because of the weakened d–p orbital hybridization. These findings provide fundamental insights into tuning the electronic properties of moiré superlattices with large twist angles.