Graphene reveals a super-rare form of magnetism when 3 layers are joined together


For something that exists in only two dimensions, Graphene seems to be everywhere. The super-thin ‘wonder material’ is renowned not only for its incredible strength, but also for its unique, often surprising blend of thermal and electromagnetic properties.

In recent times, many of the strangest experimental discoveries have been made in Graphene research when scientists stack individual layers of Graphene on top of each other. When ordinary materials combine in this way, not much happens, but even laying a few sheets of graphene together produces unusual and unexpected electronic states.

Now, a new study led by researchers from Columbia University and the University of Washington reveals another phenomenon of such behavior when graphene’s one-atom-thick latitudes are exposed to each other.

“We wondered what would happen if we combined graphene monolayers and bilayers in a twisted three-layer system,” says physicist Corey Dean of Columbia University.

“We found that the number of graphene layers placed these composite materials with some exciting new properties that had not been seen before.”

Investigating the effects of graphene layering in recent years, scientists discovered that none of the layers ever rotated slightly – so that the two sheets were resting at slightly offset angles – forming a twisted ‘magic angle’ structure. Is known, which can alternate between being an insulator and a superconductor (either blocking the electricity flowing through the material, or facilitating it without resistance).

In the new work, Dean and his team experimented with a three-layer Graphene system, which was constructed from a single-layered sheet, stacked on top of a bilayer sheet, and then turned about 1 degree.

When subjected to extremely cold temperatures, the twisted monolayer-bilayer graphene (tMBG) system, a few degrees warmer than absolute zero, exhibits an array of insulating states, which are then applied by the electric field applied to the structure. Can be controlled.

Depending on the direction of the applied electric field, the insulation capacity of the TMBG changed, akin to twisted graphene when the field monolayer sheet was pointed.

When the sphere was reversed, however, the insulating state resembled that of a four-layer graphene structure composed of a twisted double bilayer system, pointing to the bilayer sheet.

Although not all the team got it. During the experiments, the team only discovered a rare form of recently discovered magnetism.

The researchers write in their paper, “We observe the emergence of one-quarter filler of the conduction band, and electrically tunable ferromagnetism in an associated anomalous hall.”

The Hall effect traditionally refers to when the voltage can be deflected by the presence of a magnetic field, and a related phenomenon called the quantum Hall effect is observed in graphene-like two-dimensional electron systems – creating a discrepancy where the effect The amplification of K increases. Quantitative step, not a straight, linear increase.

Recent research has uncovered this magnetic behavior in graphene systems incorporating crystals of boron nitride.

Here, for the first time, however, physicists have caused the same discrepancy, only this time, they have somehow done it to Graphene themselves, which are some of the atoms we see.

“Pure carbon is not magnetic,” Yankowitz says. “Remarkably, we can engineer this property by arranging our three Graphene sheets at just the right turning angles.”

The findings are stated in Nature physics.

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