2D Mater. 5, 041008 (2018)

Understanding the nanoscale structure of materials has always been an important problem, but recent observations of superconductivity in twisted bilayer graphene with a moiré pattern make it particularly urgent for this material. A substantial advance has been made by Oleg Ovchinnikov and collaborators by combining very sensitive electron microscopy techniques with computational modelling to obtain a three-dimensional map of the crystal lattice.

Crucially, they were able to determine not only the lateral position of all the atoms from the electron microscopy, but also the height of the ripples from density functional theory calculations. This complete characterization of the material means that local relaxation induced by the bilayer moiré pattern can be distinguished from large-scale strain effects. The former may be vital in understanding the superconductivity, while the latter are important because they have a detrimental effect on conventional transport properties.