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.

[1] Cao, Y. et al. Nature 556, 43 (2018).