Exploration toward a new stacking-pressure phase diagram in bilayer AA- and AB-MoS2

The phase diagram serves as a blueprint for designing the structure of a material, offering a comprehensive representation of its different phases under specific conditions, such as temperature and pressure. In the realm of two-dimensional (2D) materials, stacking order can play a crucial role in controlling and inducing phase transitions. However, in studying phase diagrams for 2D materials, the exploration of stacking degree of freedom has largely been overlooked, limiting our understanding and hindering future applications. Here, we experimentally explore the interplay of stacking and pressure degrees of freedom in revealing unique phase transitions in bilayer MoS2 with two different stacking configurations. In AA stacking, interlayer sliding and asymmetric intralayer compressing precede intralayer rotation, while in AB stacking, asymmetric intralayer compressing and intralayer distortion occur simultaneously. Under further elevated pressure, the bilayer system transitions into 1T′ phase before amorphization. Our findings offer valuable insights for creating comprehensive phase diagrams and exploring exotic phases as well as phase transitions of 2D materials in a broader parameter space.