Something that largely exists in just two dimensions, graphene seems everywhere. The super-thin ‘wonder material’ is famous not only for its incredible strength, but also for its unique, often surprising combination in thermal and electromagnetic properties.
In recent times, graphene research has led to many bizarre experimental discoveries when scientists put different layers of graphene on top of each other. Not much happens when ordinary materials are assembled like this, but putting a few sheets of graphene together also produces an unusual and unexpected electronic state.
Now, a new study led by researchers at Columbia University and Washington University in Washington has found another phenomenon of this type of behavior when an atom-thick lattice of graphene comes in contact with each other.
“We wondered what would happen if we combined graphene monolayers and bilayers into a twisted three-tier system,” says Corey Dean, a physicist at Columbia University.
“We’ve found that a number of different graphene layers provide this composite material with some exciting new properties that haven’t been seen before.”
In recent years, while investigating the effects of graphene layering, scientists have discovered that any layer can bend slightly – so that both sheets are resting at a slightly offset angle – producing what is known as a twisted ‘magic angle’ structure. , Alternating between being an insulator and a superconductor (either blocking electricity flowing from the material, or facilitating it without any resistance).
In the new task, Dean and his team experimented with a three-tiered graphene system consisting of a single monolayer sheet stacked on top of a boiler sheet and then turned about 1 degree.
When subjected to extremely cold temperatures, the absolute zero to somewhat hot, curved monolayer-bilayer graphene (TMBG) system featured an array of insulating states, which could be controlled by the electric field to which the composition was applied.
Depending on the direction of the applied electric field, the insulation capacity of the TMBG changed, while the twisted bilayer graphene-like field pointed to the monolayer sheet.
When the field was flattened, however, pointing to the bilayer sheet, the insulating state resembles a four-layer graphene structure composed of a twisted double bilayer system.
However, not all of those teams were found. During the experiments, the team discovered a rare form of magnetism that was recently discovered.
“We observe the emergence of electrically tunable ferromagnetism on a quarter fill of the conduction band, and the associated anomalous Hall Hall effect,” the researchers wrote in their paper.
The Hall effect is traditionally referred to when voltage is ignored by the presence of a magnetic field, and a related phenomenon called a quantum Hall effect – found in a graphene-like two-dimensional electron system – produces an anomaly where the amplitude of the effect increases. Happens. Quantitative measures, not in straight, linear growth.
Recent research has uncovered this magnetic behavior in graphene systems containing crystals of boron nitride.
Here, for the first time, however, physicists have created a similar discrepancy, only this time, that they have somehow done it manually with graphene, something that the atom is dealing with us.
“Pure carbon is not magnetic,” says Yankovitz. “Significantly, we can engineer this property by simply arranging three graphene sheets at right twist angles.”
These findings are reported Nature Physics.