Nav: Home

OU physicists show novel Mott state in twisted graphene bilayers at 'magic angle'

June 19, 2019

A University of Oklahoma physics group sheds light on a novel Mott state observed in twisted graphene bilayers at the 'magic angle' in a recent study just published in Physical Review Letters. OU physicists show the Mott state in graphene bilayers favors ferromagnetic alignment of the electron spins, a phenomenon unheard of in conventional Mott insulators, and a new concept on the novel insulating state observed in twisted graphene bilayers.

"We are trying to understand the nature of the Mott state in this system," said Bruno Uchoa, associate professor in the Homer L. Dodge Department of Physics and Astrophysics. "The Mott state we proposed is an insulating state that may lead to superconductivity in some conditions, yet is different from Mott states observed in other systems. There are fundamental differences, however, and this is what we are studying."

Mott physics has been extensively investigated in the last decades in high-temperature cuprate superconductors - materials that in some conditions can transmit charge currents at relatively high temperature without producing any heat dissipation. In the Mott phase, however, the motion of charge carriers is confined by their strong mutual electric repulsion, which leads to insulating behavior, when a material is unable to conduct any electricity.

It also leads to anti-ferromagnetism, a state where the spins of two electrons sitting next to each other are anti-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 Mott state in graphene departs from other known examples in fundamental ways.

Using two sheets of graphene twisted at a very small angle, known as the 'magic angle,' the system correlates with properties seen in high-temperature superconductors. Graphene is made of carbon and the thinnest material in the universe, only 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 lattice constraints imposed by the small twist angle can strongly favor parallel alignment of the electronic spins even when electrons are strongly repelling each other. The OU physicists proposed a novel Mott state where these electrons behave in ways not seen before.

"Twisted graphene bilayers are very promising for a variety of technological applications in nanodevices," said Kangjun Seo, a postdoctoral researcher in the OU group, who was first author on the study. "This is a very interesting and important physical system."
-end-
The OU paper, "Ferromagnetic Mott State in Twisted Graphene Bilayers at the Magic Angle," recently was published in Physical Review Letters. A National Science Foundation grant funded the OU research. For more information about this study, contact Uchoa at Uchoa@ou.edu.

University of Oklahoma

Related Graphene Articles:

New 'brick' for nanotechnology: Graphene Nanomesh
Researchers at Japan advanced institute of science and technology (JAIST) successfully fabricated suspended graphene nanomesh (GNM) by using the focused helium ion beam technology.
Flatter graphene, faster electrons
Scientists from the Swiss Nanoscience Institute and the Department of Physics at the University of Basel developed a technique to flatten corrugations in graphene layers.
Graphene Flagship publishes handbook of graphene manufacturing
The EU-funded research project Graphene Flagship has published a comprehensive guide explaining how to produce and process graphene and related materials (GRMs).
How to induce magnetism in graphene
Graphene, a two-dimensional structure made of carbon, is a material with excellent mechani-cal, electronic and optical properties.
Graphene: The more you bend it, the softer it gets
New research by engineers at the University of Illinois combines atomic-scale experimentation with computer modeling to determine how much energy it takes to bend multilayer graphene -- a question that has eluded scientists since graphene was first isolated.
How do you know it's perfect graphene?
Scientists at the US Department of Energy's Ames Laboratory have discovered an indicator that reliably demonstrates a sample's high quality, and it was one that was hiding in plain sight for decades.
Graphene is 3D as well as 2D
Graphene is actually a 3D material as well as a 2D material, according to a new study from Queen Mary University of London.
How to purify water with graphene
Scientists from the National University of Science and Technology 'MISIS' together with their colleagues from Derzhavin Tambov State University and Saratov Chernyshevsky State University have figured out that graphene is capable of purifying water, making it drinkable, without further chlorination.
Decoupled graphene thanks to potassium bromide
The use of potassium bromide in the production of graphene on a copper surface can lead to better results.
1 + 1 does not equal 2 for graphene-like 2D materials
Physicists from the University of Sheffield have discovered that when two atomically thin graphene-like materials are placed on top of each other their properties change, and a material with novel hybrid properties emerges, paving the way for design of new materials and nano-devices.
More Graphene News and Graphene Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Meditations on Loneliness
Original broadcast date: April 24, 2020. We're a social species now living in isolation. But loneliness was a problem well before this era of social distancing. This hour, TED speakers explore how we can live and make peace with loneliness. Guests on the show include author and illustrator Jonny Sun, psychologist Susan Pinker, architect Grace Kim, and writer Suleika Jaouad.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.