Twist-Angle Dependent Properties of Bilayer MoS₂

Angeli and MacDonald reported a superlattice-imposed Dirac band in twisted bilayer molybdenum disulphide (tBL MoS₂) for small twist angles towards the R^M_h (parallel) stacking. Using a hierarchical set of theoretical methods, we show that the superlattices differ for twist angles with respect to metastable R^M_h (0°) and lowest-energy H^h_h (60°) configurations. When approaching R^M_h stacking, identical domains with opposite spatial orientation emerge. They form a honeycomb superlattice, yielding Dirac bands and a lateral spin texture distribution with opposite-spin-occupied K and K’ valleys. Small twist angles towards the H^h_h configuration (60°) generate H^h_h and H^X_h stacking domains of different relative energies and, hence, different spatial extensions. This imposes a symmetry break in the moiré cell, which opens a gap between the two top-valence bands, which become flat already for relatively small moiré cells. The superlattices impose electronic superstructures resembling graphene and hexagonal boron nitride into trivial semiconductor MoS₂.<br/>Changes in the twist angle not only affect electronic properties of the material, but also affect the interactions with intercalated species. Here, we show that the hydrogen atom diffusion coefficient strongly changes when twist angle changes from H^h_h to R^M_h stackings, up to one order of magnitude. This can be utilized when designing materials for directional transport of hydrogen or novel fuel cells.