Designing flat bands, localized and itinerant states in TaS₂ trilayer heterostructures

Stacking and twisting van der Waals materials provides a powerful tool to engineer quantum matter. For instance, 1T-TaS₂ monolayers are Mott insulators, whereas layered 1H-TaS₂ is metallic and superconducting; thus, the T/H bilayer, where heavy fermions and unconventional superconducting phases are expected from localized spins (1T) coexisting with itinerant electrons (1H), has been intensively studied. However, recent studies revealed significant charge transfer that questions this scenario. Here, we propose a T/T/H trilayer heterostructure where the T/T bilayer is a flat-dispersion band insulator with localized electrons, whereas the 1H layer remains metallic with a weak spin polarization. Varying the T/T stacking configuration tunes the flat-band filling, enabling a crossover from a doped-Mott regime to a Kondo-like state. Such a trilayer heterostructure provides, therefore, a rich novel platform to study strong correlation phenomena and unconventional superconductivity.