Think you know everything about a material? Try giving it a twist—literally. That’s the main idea of an emerging field in condensed matter physics called “twistronics,” which has researchers drastically changing the properties of 2D materials, like graphene, with subtle changes—as small as going from a 1.1° to 1.2°—in the angle between stacked layers.
Twisted layers of graphene, for example, have been shown to behave in ways that single sheets have not, including acting like magnets, like electrical superconductors, or like a superconductor’s opposite, insulators, all due to small changes in the twist angle between sheets.
In theory, you could dial in any property by turning a knob that changes the twist angle. The reality, however, isn’t so straightforward, says Columbia physicist Cory Dean. Two twisted layers of graphene can become like a new material, but exactly why these different properties manifest is not well understood, let alone something that can be fully controlled yet.
Dean and his lab have come up with a simple new fabrication technique that may help physicists probe the fundamental properties of twisted layers of graphene and other 2D materials in a more systematic and reproducible way. Writing in Science, they use long “ribbons” of graphene, rather than square flakes, to create devices that offer a new level of predictability and control over both twist angle and strain.
Graphene devices have typically been assembled from atom-thin flakes of graphene that are just a few square millimeters. The resulting twist angle between the sheets is fixed in place, and the flakes can be tricky to layer together smoothly.
2023-08-11 11:24:03
Original from phys.org