Magnetic and ferroelectric phase diagram of twisted CrI$_3$ layers

Twisting layers provide a rich ore for exotic physics in low dimensions. Despite the abundant discoveries of twistronics from the aspect of electronic structures, ferroic moiré textures are more plain and thus less concerned. Rigid lattice models are straightforward which can give a rough but intuitional description in most cases. However, taking CrI$_3$ as a model system, here we will demonstrate that the interlayer stacking potential can spontaneously lead to structural relaxation, which plays a vital role to understand the ferroicity in the twisted superlattices. The magnetic ground state is sensitive to the stacking mode and twisting angles, which can be seriously affected by the structural relaxation. In particular, the expected magnetic bubbles are annihilated in its bilayer. In contrast, due to topological protection, the ferroelectric vortices are more robust to structural relaxation, as well as twisting angle and thickness.Due to the universal existence of spontaneous structural relaxation in twisted superlattices, our work may lead to a general revisitation of emerging physics of twistronics.