A widely used type of microscopy can reveal the structure of 2D ‘wonder materials’ in superb detail.
Take two carbon sheets, each only one atom thick. Stack them, then rotate them so that their crystal structures are slightly misaligned. The resulting structure, called a ‘twisted bilayer’, can have surprising properties, such as superconductivity, making this and similar structures of great interest to physicists.
To image a type of twisted bilayer called a superlattice, Abhay Pasupathy at Columbia University in New York City and his collaborators used a room-temperature technique that applies alternating electric fields to a material, creating slight changes in the material’s surface. A fine probe detects these changes to reveal the material’s topography.
The bilayer contains tile-shaped regions where its two crystalline sheets are close to an energetically favourable alignment. Interesting physics arises from the interaction between the tiles and the material’s electrons — but the details have been inaccessible to scientists relying on more-standard forms of room-temperature microscopy, which typically cannot image the tiles.
The new method not only reveals the tiles but shows, unexpectedly, that the electrons in the material move to the edges of the tiles.