Nav: Home

Artificial magnetic field produces exotic behavior in graphene sheets

November 29, 2018

A simple sheet of graphene has noteworthy properties due to a quantum phenomenon in its electron structure named Dirac cones in honor of British theoretical physicist Paul Dirac (1902-1984), who was awarded the Nobel Prize for Physics in 1933.

The system becomes even more interesting if it comprises two superimposed graphene sheets, and one is very slightly turned in its own plane so that the holes in the two carbon lattices no longer completely coincide.

For specific angles of twist, the bilayer graphene system displays exotic properties such as superconductivity (zero resistance to electrical current flow).

A new study conducted by Brazilian physicist Aline Ramires with Jose Lado, a Spanish-born researcher at the Swiss Federal Institute of Technology (ETH Zurich), shows that the application of an electrical field to such a system produces an effect identical to that of an extremely intense magnetic field applied to two aligned graphene sheets.

An article on the study has recently been published in Physical Review Letters and was selected to feature on the issue's cover. It can also be downloaded from the arXiv platform.

Ramires is a researcher at São Paulo State University's Institute of Theoretical Physics (IFT-UNESP) and the South American Institute for Fundamental Research (ICTP-SAIFR). She is supported by São Paulo Research Foundation - FAPESP through a Young Investigator grant.

"I performed the analysis, and it was computationally verified by Lado," Ramires told. "It enables graphene's electronic properties to be controlled by means of electrical fields, generating artificial but effective magnetic fields with far greater magnitudes than those of the real magnetic fields that can be applied."

The two graphene sheets must be close enough together for the electronic orbitals of one to interact with the electronic orbitals of the other, she explained.

This means a separation as close as approximately one angstrom (10-10 meter or 0.1 nanometer), which is the distance between two carbon atoms in graphene.

Another requirement is a small angle of twist for each sheet compared to the other - less than one degree (α<<1°).

Although entirely theoretical (analytical and numerical), the study has clear technological potential, as it shows that a versatile material such as graphene can be manipulated in hitherto unexplored regimes.

"The artificial magnetic fields proposed previously were based on the application of forces to deform the material. Our proposal enables the generation of these fields to be controlled with much greater precision. This could have practical applications," Ramires said.

The exotic states of matter induced by artificial magnetic fields are associated with the appearance of "pseudo-Landau levels" in graphene sheets.

Landau levels - named after the Soviet physicist and mathematician Lev Landau (1908-1968), Nobel Laureate in Physics in 1962 - are a quantum phenomenon whereby in the presence of a magnetic field, electrically charged particles can only occupy orbits with discrete energy values. The number of electrons in each Landau level is directly proportional to the magnitude of the applied magnetic field.

"These states are well-located in space; when particles interact at these levels, the interactions are much more intense than usual. The formation of pseudo-Landau levels explains why artificial magnetic fields make exotic properties such as superconductivity or spin liquids appear in the material," Ramires said.
About São Paulo Research Foundation (FAPESP)

The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships, and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. For more information:

Fundação de Amparo à Pesquisa do Estado de São Paulo

Related Graphene Articles:

New chemical method could revolutionize graphene
University of Illinois at Chicago scientists have discovered a new chemical method that enables graphene to be incorporated into a wide range of applications while maintaining its ultra-fast electronics.
Searching beyond graphene for new wonder materials
Graphene, the two-dimensional, ultra lightweight and super-strong carbon film, has been hailed as a wonder material since its discovery in 2004.
New method of characterizing graphene
Scientists have developed a new method of characterizing graphene's properties without applying disruptive electrical contacts, allowing them to investigate both the resistance and quantum capacitance of graphene and other two-dimensional materials.
Chemically tailored graphene
Graphene is considered as one of the most promising new materials.
Beyond graphene: Advances make reduced graphene oxide electronics feasible
Researchers have developed a technique for converting positively charged (p-type) reduced graphene oxide (rGO) into negatively charged (n-type) rGO, creating a layered material that can be used to develop rGO-based transistors for use in electronic devices.
The Graphene 2017 Conference connects Barcelona with the international graphene-based industry
This prestigious Conference to be held at the Barcelona International Convention Centre (March 28-31) aims to bring together academia and industry to integrate new graphene technologies into practical applications.
Graphene from soybeans
A breakthrough by CSIRO-led scientists has made the world's strongest material more commercially viable, thanks to the humble soybean.
First use of graphene to detect cancer cells
By interfacing brain cells onto graphene, researchers at the University of Illinois at Chicago have shown they can differentiate a single hyperactive cancerous cell from a normal cell, pointing the way to developing a simple, noninvasive tool for early cancer diagnosis.
Development of graphene microwave photodetector
DGIST developed cryogenic microwave photodetector which is able to detect 100,000 times smaller light energy compared to the existing photedetectors.
Adding hydrogen to graphene
IBS researchers report a fundamental study of how graphene is hydrogenated.

Related Graphene Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Failure can feel lonely and final. But can we learn from failure, even reframe it, to feel more like a temporary setback? This hour, TED speakers on changing a crushing defeat into a stepping stone. Guests include entrepreneur Leticia Gasca, psychology professor Alison Ledgerwood, astronomer Phil Plait, former professional athlete Charly Haversat, and UPS training manager Jon Bowers.
Now Playing: Science for the People

#524 The Human Network
What does a network of humans look like and how does it work? How does information spread? How do decisions and opinions spread? What gets distorted as it moves through the network and why? This week we dig into the ins and outs of human networks with Matthew Jackson, Professor of Economics at Stanford University and author of the book "The Human Network: How Your Social Position Determines Your Power, Beliefs, and Behaviours".