Multilayer graphene can act as a superconductor when several graphene sheets are layered in a specific stacking order.
Multilayer graphene with a specific stacking order of the ABC sequence (see Fig. 1b) is theoretically predicted to exhibit flat dispersion of the electronic band at the K points of the Brillouin zone, which would result in superconducting properties. However, this specific ABC stacked multilayer graphene cannot be made by the scotch tape technique, and growing it on a substrate is still very challenging.
The peculiar properties of ultrathin single crystal graphitic layers on silicon carbide (SiC) substrates, demonstrated by Professor Rositsa Yakimova in 2002 triggered further intensive research on this material which ideally matched with the demonstration of graphene by the Manchester group in 2004.1
Graphene grown on silicon carbide
Among the diversity of graphene fabrication techniques, the thermal decomposition of SiC is regarded as a highly promising method for the production of device-quality graphene. Researchers at Linköping University (LiU) have been working on SiC since the 1990s. In particular, Yakimova is an expert in the sublimation growth of SiC crystals and, as a natural development, she has pioneered a novel method for the fabrication of large area homogeneous epitaxial graphene on SiC, and since 2008 she has led the research of graphene on SiC at Linköping University. In 2011, Yakimova and her co-workers founded GraphenSiC AB, a spin-off company manufacturing high quality wafer scale epitaxial graphene on SiC substrate. GraphenSiC fabricates monolayer epitaxial graphene on SiC for a large variety of applications.
ABC-stacked four-layer graphene
Recently, researchers collaborating with Yakimova have developed a method to grow the ABC-stacked multilayer graphene on cubic silicon carbide (3C-SiC).2; 3
The main challenge involved in growing large-area multilayer graphene is related to solving the problem of the SiC step bunching, which is defined as the energy driven formation of high steps (a few unit cells of SiC, ranging from a few nanometres to tens of nanometres) and wide terraces (ranging from a few hundreds of nanometres to micrometres).
The group led by Dr Jianwu Sun has recently solved the elimination of the step bunching issue and has succeeded in growing four-layer graphene on 3C-SiC by a controlled technology. Their further experimental and theoretical studies verify the existence of the ABC stacking sequence in four-layer graphene, which plays an important role in superconductivity and many other exotic phases of matter.
- Phys. Rev. B66, 235422
- Nano Letters, 2018, 18, Pages 5862–5866, DOI: 10.1021/acs.nanolett.8b02530
- Carbon, 2018, 140, Pages 533-542, https://doi.org/10.1016/j.carbon.2018.08.042
Department of Physics, Chemistry and Biology (IFM)