The electrical properties of graphene can be completely changed in a simple way, as found out by Yuan Cao, Massachusetts Institute of Technology (MIT), Cambridge, USA, and his colleagues.
Two graphene layers are rotated by 1.1° to each other. At this angle, the graphene lattices form a kind of Moiré pattern that leads to unusual interactions between the electrons of the carbon atoms. The material thus behaves like a so-called Mott insulator – a material that no longer conducts electricity despite half-filled electron bands. The graphene grid can switch abruptly from the insulator to the resistively conducting superconductor. For this, it a small voltage has to be applied to the mutually twisted graphene layers. The density of the charge carriers is several orders of magnitude lower than for typical 2D superconductors.
These results open up many possibilities. For example, graphene could become a new platform for unconventional superconductivity research.
- Correlated insulator behaviour at half-filling in magic-angle graphene superlattices,
Yuan Cao, Valla Fatemi, Ahmet Demir, Shiang Fang, Spencer L. Tomarken, Jason Y. Luo, J. D. Sanchez-Yamagishi, K. Watanabe, T. Taniguchi, E. Kaxiras, R. C. Ashoori, P. Jarillo-Herrero,
Nature 2018.
https://doi.org/10.1038/nature26154
