Three-dimensional flat bands and possible interlayer triplet pairing superconductivity in the alternating twisted NbSe₂ moiré bulk

Moiré superlattices hosting flat bands and correlated states have become a central focus in condensed matter research. Using first-principles calculations, we investigate three-dimensional flat bands in alternating twisted NbSe₂ moiré bulk structures, which exhibit stronger interlayer interactions than twisted bilayer configurations. Our results show that moiré bulks undergo spontaneous large-scale structural relaxation, leading to the formation of remarkably flat energy bands at twist angles ≤7.31°. The k_z-dependent dispersion of these flat bands across different moiré bulks highlights their intrinsic three-dimensional character. Moreover, the presence of out-of-plane mirror symmetry in these moiré bulk structures indicates potential interlayer triplet superconducting pairing mechanisms, distinct from those in twisted bilayer systems. This work opens new avenues for exploring three-dimensional flat bands in other moiré bulk systems.