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Physicist shows new Mott states in twisted graph-bilayers at "magic angle"



  OU physicists show new Mott states in twisted graph bilayers at
The graph is made of carbon and is the thinnest material in the universe, just one atom thick. Credit: University of Oklahoma

A University's Oklahoma Physics Group highlights a new moth condition observed in twisted graph bilayers at a "magical angle" in a recent study recently published in Physical Review Letters . OU physicists show the moth state of the graph-bilayer's favor ferromagnetic alignment of the electron spin, a phenomenon not appreciated in conventional Mott isolators and a new concept on the new isolating state observed in twisted graph-bilayers.

"We are trying to understand the nature of the Mott state in this system," says Bruno Uchoa, Associate Professor of Homer L. Dodge Department of Physics and Astrophysics. "The mock state we proposed is an insulating state that can lead to superconductivity under certain conditions, but is different from the moth states observed in other systems. However, there are fundamental differences, and this is what we are studying."

Many physics have been extensively investigated over the past few decades in high temperature copper superconducting materials which, under certain conditions, can transmit charge currents at relatively high temperature without producing any heat dissipation. However, in the Mott phase, the charge carrier's movement is limited by its strong electrical interference, which leads to insulating behavior when a material cannot conduct any electricity.

It also leads to anti-ferromagnetism, a state where the spin of two electrons sitting next to each other is parallel. The latter property is the result of the Pauli exclusion principle, one of the many exotic properties of quantum mechanics, which states that the two electrons cannot occupy the same quantum state. The new study shows that the moth state in the graph deviates from other known examples of basic ways.

The use of two sheets of graphene spun at a very small angle, known as "magic angle", correlates the system with properties seen in high-temperature superconductors. The graph is made of coal and the thinnest material in the universe, just one atom thick. The material is like a honeycomb lattice, so two layers twisted at a very small angle result in the electrons moving differently. The new work shows that grid constraints introduced by the small angle of rotation can greatly favor the parallel alignment of the electronic spins even when the electrons strongly reject each other. The OU physicists suggested a new Mott state where these electrons behave in ways not previously shown.

"Twisted graphene bilayers are very promising for a variety of technical applications in nanodevices," said Kangjun Seo, a postdoctoral researcher in the OU group, who was the first author of the study. "This is a very interesting and important physical system." The OU paper, "Ferromagnetic Mott State in Twisted Graphene Bilayers at the Magic Angle", was recently published in Physical Review Letters .


Team finds Wigner crystal-not Mott-isolator-in "magic angle" graph


More information:
Kangjun Seo et al. Ferromagnetic Moth Condition in Twisted Graphene Bilayers at Magic Angle, Physical Review Letters (201
9). DOI: 10,1103 / PhysRevLett.122.246402

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University of Oklahoma




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Physicist shows new Mott states in twisted graph-bilayers at "magical angle" (2019, June 19)
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