Exotic magnetic properties discovered in multilayer graphene – Science

TASS, October 12. Physicists have found that multilayer structures of three sheets of graphene exhibit unusual magnetic properties. They appear or disappear abruptly at the slightest shift in the position of the layers of this material. An article with the results of the work of scientists was published by a scientific journal Nature Physics.

“Pure carbon has no magnetic properties. However, as we found out, this can be achieved by taking three sheets of graphene and stacking them on top of each other at a certain angle.” told one of the authors of the work, professor at Columbia University Matthew Yankovich.

Graphene is a single layer of carbon atoms that are interconnected by a structure of chemical bonds similar to a honeycomb. For obtaining and studying the first samples of graphene, Russian immigrants Konstantin Novoselov and Andrey Geim received the Nobel Prize in physics in 2010.

Two years ago, physicists at the Massachusetts Institute of Technology (MIT) accidentally turned graphene into an exotic “insulator-superconductor” by gluing two pieces of this material together at a certain angle and getting a peculiar moire pattern… With graphene sheets in this position, carbon atoms begin to strongly influence how electrons move inside this entire structure.

Due to this, due to the rotation of one of the graphene sheets at a certain angle, current carriers begin to move without energy loss, like electron pairs in superconductors. For small deviations from this angle, an insurmountable barrier for other particles arises due to electron interactions. The substances in which this happens are called by physicists “Mott insulators”.

Magnetic graphene

Professor Jankovic and his colleagues have discovered even more surprising properties in such materials. They experimented with moiré patterns, which occur when not two, but three sheets of graphene are superposed. Putting them on top of each other at different angles, scientists found out how the properties of such structures change when the angle of rotation of the sheets and their position relative to each other change.

In three-layer structures, which consisted of two perfectly aligned layers of graphene and a single sheet of this carbon material superimposed on top of them, scientists discovered not only interesting electrical characteristics, but also magnetic properties.

Jankovic and his colleagues found that they arose when this single sheet was rotated with respect to the two-layer graphene structure at an angle of 0.89 °. At the same time, interestingly, the magnetic properties appeared only after scientists applied an electric field to the two-layer part of this structure. Moreover, if the same field was applied to a single sheet, then all magnetic properties disappeared.

Further experiments showed that these magnetic properties had a rather exotic nature. They were not associated with individual electrons, but with large groups of these particles. In addition, scientists have found that the magnetic properties of individual regions inside a three-layer graphene can be flexibly changed by “pumping” them with additional charge carriers.

Due to this, such structures can be used as a basis for creating qubits – elementary cells of quantum computers, and quantum computing, as well as new information storage systems with a very high density of information recording. Such materials will require relatively little energy to operate.

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