Global control of stacking order phase transition by doping and electrical field in few-layer graphene.

The layer stacking order has profound effects on physical properties of two-dimensional (2D) van der Waals heterostructures. For example, graphene multilayers can have distinct electronic band structures and exhibit completely different behaviors depending on their stacking orders. Fascinating physical phenomena -- such as correlated insulators, superconductors, and ferromagnetism -- can also emerge with a periodic variation of the layer stacking order, which is known as the moiré superlattice in van der Waals materials. In this work, we realize global phase transition between different graphene layer stacking orders and elucidate its microscopic origin. We experimentally determine the energy difference between different stacking orders with the accuracy of eV/atom. We reveal that both the carrier doping and the electrical field can drive the layer stacking phase transition through different mechanisms: The carrier doping can change the energy difference due to a non-negligible work function difference between different stacking orders. The electrical field, on the other hand, induces a band gap opening in ABC stacked graphene and hence changes the energy difference. Our findings provide a fundamental understanding of the electrically driven stacking order phase transition in few-layer graphene and demonstrate a reversible and non-invasive method to globally control the stacking orders.