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Physicists show the novel Mott state in twisted graphene bilayers at magical angles



  OU physicists show a novel Mott state in twisted graphene bilayers at magic angles.
Graphene is made of carbon and is the thinnest material in the universe, just one atom thick. Credit: University of Oklahoma

A physics group from the University of Oklahoma reviewed a novel Mott state observed in twisted graphene bilayers at the "magic angle" in a recent study published in Physical Review Letters . OU physicists show that the Mott state in graphene bilayers favors ferromagnetic alignment of electron spins, a phenomenon unknown in conventional Mott insulators, and a novel concept for the novel isolation state observed in twisted graphene bilayers ,

"We try to understand the nature of the Mott state in this system," said Bruno Uchoa, adjunct professor at the Homer L. Dodge Department of Physics and Astrophysics. "The Mott state we proposed is an insulating state that can lead to superconductivity under certain conditions, but differs from the Mott states observed in other systems, but there are fundamental differences, and that's what we're investigating."

Mott Physics has been extensively studied in high-temperature cuprate superconductors over the past few decades ̵

1; materials that can under certain conditions transfer charge currents at relatively high temperatures without heat dissipation. However, in the Mott phase, the motion of charge carriers is limited by their strong mutual electrical repulsion, resulting in insulating behavior when a material can not conduct electricity.

It also leads to antiferromagnetism, a state where the spins of two juxtaposed electrons are antiparallel. 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 can not occupy the same quantum state. The new study shows that the graphene Mott state differs fundamentally from other known examples.

Using two graphene sheets twisted at a very small angle, the so-called magic angle, the system correlates with properties seen at high angles – temperature superconductors. Graphene is made of carbon and is the thinnest material in the universe, just one atom thick. The material is like a honeycomb grid, so two layers twisted at a very small angle cause the electrons to move differently. The new work shows that lattice constraints imposed by the small twist angle can strongly favor the parallel alignment of electronic spins, even when electrons repel strongly. The OU physicists proposed a novel Mott state in which these electrons behave in unprecedented ways.

"Twisted graphene bilayers are promising for a variety of nano-technology applications," said Kangjun Seo, a postdoctoral fellow in the OU group. who was the first author of the study. "This is a very interesting and important physical system."

The OU publication "Ferromagnetic Mott State in Twisted Graphene Bilayers at the Magic Angle" was recently published in Physical Review Letters (19459010).


Team finds Wigner crystal – not Mott insulator – in the & # 39; magic angle & # 39; graph


Further information:
Kangjun Seo et al. Ferromagnetic Mott state in twisted graphene bilayers at magical angles, Physical Review Letters (2019). DOI: 10.1103 / PhysRevLett.122.246402

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University of Oklahoma




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Physicists show the novel Mott state in twisted graphene bilayers at magical angles (2019, June 19)
retrieved on 19 June 2019
from https://phys.org/news/2019-06-physicists-mott-state-graphene-bilayers.html

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