Recently, scientists at Columbia University and the University of Washington discovered that the stacking and twisting of a three-layered graphene structure can unlock a variety of alien electronic states, including a rare form of magnetism.
The work was inspired by recent studies of twisted monolayers or twisted bilayers of graphene, comprising two or four total sheets. These materials have been shown to harbor a set of unusual electronic states driven by strong interactions between electrons.
Cory Dean, professor of physics at Columbia University, said: âWe wondered what would happen if we combined monolayers and bilayers of graphene in a twisted three-layer system. We have found that varying the number of graphene layers gives these composite materials exciting new properties that have never been seen before. “
For the study, the scientists stacked a monolayer sheet of graphene on top of a bilayer sheet and twisted them about 1 degree. At temperatures a few degrees above absolute zero, the group of insulating, non-conducting states are powered by strong associations between electrons. They further discovered that these states could be controlled by applying an electric field to the graphene sheets.
Assistant Professor Matthew Yankowitz said: “We have learned that the direction of an applied electric field is very important.”
Pointing the electric field towards the single-layered graphene sheet resulted in a twisted bilayer graphene. When the scientists reversed the direction of the electric field and pointed it at the bilayer graphene sheet, it mimicked twisted bilayer graphene, the four-layered structure.
The team also discovered new magnetic states in the system. In addition to magnetism, the study revealed signs of topology in the structure. As with tying different types of knots in a rope, the topological properties of the material can lead to new forms of information storage, which âcan be a platform for quantum computing or new types of storage applications. energy saving data.
Professor Xiaodong Xu noted, “As with tying different types of knots in a rope, the topological properties of the material can lead to new forms of information storage, which” can be a platform for quantum computing or new types of storage applications. energy efficient data. “
Scientists are currently busy understanding the fundamental properties of the new states they have discovered.
- Electrically tunable correlated and topological states in twisted monolayer-bilayer graphene, Nature Physics (2020). DO I: 10.1038 / s41567-020-01062-6