Flat Bands and Correlated States in H-stack Twisted Bilayer Transition Metal Dichalcogenides

Flat electronic bands, where the electron energy is nearly independent of the crystal momentum, greatly enhance Coulomb interactions and can host a variety of strongly correlated quantum phases. Two-dimensional moiré superlattices offer a highly tunable platform to engineer and study such flat-band systems. Here we investigate hexagonally stacked transition metal dichalcogenide homo-bilayers, in which the bandwidths of moiré mini-bands calculated by DFT are comparable to each other. Using variable-temperature microwave impedance microscopy (MIM), we observe correlated insulating states in ~57.5° twisted MoS₂ (t-MoS₂) persisting up to room temperature, consistent with recent transport studies. In contrast, no insulating behavior is detected in electron-doped t-MoSe₂ at the same twist angle down to 180 mK. Our work reveals the complexity of flat-band systems with internal degrees of freedom, which is significant in advancing our understanding of quantum phases with strong correlations.