Marta Pelc

Stackings in graphene have a pivotal role in properties to be discussed in the future, as seen in the recently found superconductivity of twisted bilayer graphene [1]. Especially interesting is the rhombohedral stacking of few-layer graphene, which reveals flat bands near the Fermi level that are associated with interesting phenomena, such as tunable conducting surface states [2]. It is also expected to exhibit spontaneous quantum Hall effect [3], surface superconductivity [4], and even topological order [5]. However, the difficulty in exploring rhombohedral graphenes is that in experiments, the alternative, hexagonal (Bernal) stacking is the most commonly found geometry and has been considered the most stable configuration for many years.

Here we reexamine this stability issue in line with current ongoing studies in various laboratories. We conducted a detailed investigation of the relative stability of trilayer graphene stackings and showed how delicate this subject is. Few-layer graphenes appear to have two basic geometries with very similar energies – rhombohedral and Bernal ones. The final stacking of the sample is determined by compressions but also anisotropic in-plane distortions [6]. Furthermore, switching between stable stackings is more clearly induced by deformations such as shear and breaking of the symmetries between graphene sublattices, which can be accessed during selective synthesis approaches. We seek a guide on how to better control – preserve or change – the stackings in multilayer graphene samples.

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2. Shi, Y. et al. Nature 584, 210–214 (2020).
3. Zhang, F. et al. Phys. Rev. Lett. 106, 156801 (2011).
4. Kopnin, N. et al. Phys. Rev. B 87, 140503 (2013).
5. Slizovskiy, S. et al. Comm. Phys. 2, 1-10 (2019).
6. Geisenhof, F. R. et al. ACS Appl. Nano. Mater. 2, 6067–6075 (2019).