Synthesis of long-range stacked rhombohedral graphene through shear and effects of temperature

The discovery of superconductivity in twisted bilayer graphene, associated to flat bands close to the Fermi level, has raised a lot of excitement. Such highly correlated states have also been observed in many layers of multilayer stacked rhombohedral graphene (RG). However, it is observed less frequently than multilayer stacked Bernal graphene (BG), so the conditions under which RG becomes more stable than BG should be determined. Here we show, using first principles calculations, that applying shear stress induces long-range rhombohedral order. The experimental conditions under which RG can be obtained are presented in a stress-angle phase diagram [1]. Then we calculate the energy difference of bulk RG and BG using different functionals, and show that the electronic temperature plays a crucial role. The stability is also studied for a finite amount of layers, and the low energy states are characterized. Our work clarifies inconsistencies in the literature, and sets the basis to add factors like doping or an electric field in first principles calculations.

[1] J. P. Nery, M. Calandra, and F. Mauri, Nano Lett. 20, 5017 (2020).