Completing the stacking–pressure phase diagram in bilayer MoS₂

Pressure-stacking phase diagrams are uniquely important for studying two-dimensional (2D) materials. However, due to experimental challenges, a complete stacking-pressure phase diagram has remained elusive. Here, we complete such phase diagram by growing both naturally-occurring (AA and AB) and artificially-created (stacking angle finely-varying between 0° and 60°) bilayer MoS₂ crystals (tBLM), and study the evolution of their Raman modes upon compression. Through detailed analysis of spectral transitions under pressure, we observe a clear contrast in the pressure-induced phase behavior of tBLM in these two categories, uncover a unique metastable phase, and discover a chevron-shaped dependence between transition pressures and the stacking axis. Based on the above findings, we construct a complete and detailed stacking-pressure phase diagram for this bilayer 2D material system. Our findings offer a new approach for exploring and understanding phase transitions in 2D materials under pressure.