Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Two-dimensional dirac materials: Structure, properties, and rarity

01.04.2015

Graphene, a two-dimensional (2D) honeycomb sheet composed of carbon atoms, has attracted intense interests worldwide because of its outstanding properties and promising prospects in both basic and applied science.

The great development of graphene is closely related to the unique electronic structure, that is, Dirac cones. The cone which represents linear energy dispersion at Fermi level gives graphene massless fermions, leading to various quantum Hall effects, ultra high carrier mobility, and many other novel phenomena and properties.


This is a scheme of 2-D materials with Dirac cones.

Credit: ©Science China Press

Dirac cone is special but might not unique to graphene. Recently, more and more 2D materials have been predicted to possess Dirac cones, such as silicene and germanene (graphene-like silicon and germanium, respectively), several graphynes (sp-sp2 carbon allotropes), and so on. But these 2D Dirac systems are so rare compared to the numerous 2D materials. A deep understanding of all known 2D Dirac systems and a strategy to seek for new ones are needed.

A new paper published in National Science Review presented the recent progress on theoretical studies of various 2D Dirac materials.

In this paper, the structural and electronic properties of graphene, silicene, germanene, graphynes, several boron and carbon allotropes, transition metal oxides, organic and organometallic crystals, square MoS2, and artificial lattices (electron gases and ultracold atoms) were summarized.

As the author stated, "most Dirac materials have spatial inversion symmetry", "Many of them are bipartite and composed of only one element", and "hexagonal honeycomb structure is common in atomic Dirac materials".

Since "the Dirac-cone structure gives graphene massless fermions, leading to half-integer/fractional/fractal quantum Hall effects, ultrahigh carrier mobility", other 2D Dirac systems were predicted to have similar properties, and some even possess new physics beyond graphene.

Based on the above discussions, the authors further investigated how Dirac points move and merge in these systems. They mentioned that strain can move the Dirac point to a new k (reciprocal) location. But "when two Dirac points with opposite Berry phases move in the k space under any perturbation and arrive at the same point, they merge and their Berry phases annihilate each other".

Moreover, the von Neumann-Wigner theorem was applied to explain the scarcity of 2D Dirac systems. Then rigorous requirements for a 2D system to achieve Dirac cones were deduced, which is related to the symmetry, parameters, Fermi level, and band overlap.

This paper noted that "Dirac cones are not only the linear energy dispersion around discrete points but also singularities in the spectrum of Hamiltonians and are topologically protected." The authors pointed out "Looking forward, we believe that more and more 2D Dirac materials will be discovered, and a thorough understanding on the existing conditions of Dirac cones is greatly helpful in seeking/designing new systems."

###

This research received funding from the National Natural Science Foundation of China (Grant No. 21373015).

See the article

Jinying Wang, Shibin Deng, Zhongfan Liu, and Zhirong Liu. "The Rare Two-Dimensional Materials with Dirac Cones".

National Science Review (March 2015) 2 (1): 22-39. (http://nsr.oxfordjournals.org/content/2/1/22.full)

The National Science Review is the first comprehensive scholarly journal released in English in China that is aimed at linking the country's rapidly advancing community of scientists with the global frontiers of science and technology. The journal also aims to shine a worldwide spotlight on scientific research advances across China.

Zhirong Liu | EurekAlert!

Further reports about: Fermi electronic structure graphene materials scientific research structure

More articles from Materials Sciences:

nachricht ADIR Project: Lasers Recover Valuable Materials
21.07.2017 | Fraunhofer-Institut für Lasertechnik ILT

nachricht High-tech sensing illuminates concrete stress testing
20.07.2017 | University of Leeds

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>