Nanotechnology Now

Our NanoNews Digest Sponsors
Heifer International

Wikipedia Affiliate Button

Home > Press > Graphene: A quantum of current - When current comes in discrete packages: Viennese scientists unravel the quantum properties of the carbon material graphene

Electron wave passing through a narrow constriction.
CREDIT: TU Wien
Electron wave passing through a narrow constriction.

CREDIT: TU Wien

Abstract:
In 2010 the Nobel Prize in physics was awarded for the discovery of the exceptional material graphene, which consists of a single layer of carbon atoms arranged in a honeycomb lattice. But graphene research did not stop there. New interesting properties of this material are still being found. An international team of researchers has now explained the peculiar behaviour of electrons moving through narrow constrictions in a graphene layer. The results have been published in the journal Nature Communications.

Graphene: A quantum of current - When current comes in discrete packages: Viennese scientists unravel the quantum properties of the carbon material graphene

Vienna, Austria | Posted on May 20th, 2016

The Electron is a Wave

"When electrical current flows through graphene, we should not imagine the electrons as little balls rolling through the material", says Florian Libisch from TU Wien (Vienna), who led the theoretical part of the research project. The electrons swash through the graphene as a long wave front, the wavelength can be a hundred times larger than the space between two adjacent carbon atoms. "The electron is not confined to one particular carbon atom, in some sense it is located everywhere at the same time", says Libisch.

The team studied the behaviour of electrons squeezing through a narrow constriction in a graphene sheet. "The wider the constriction, the larger the electron flux - but as it turns out, the relationship between the width of the constriction, the energy of the electrons and the electric current is quite complex", says Florian Libisch. "When we make the constriction wider, the electric current does not increase gradually, it jumps at certain points. This is a clear indication of quantum effects."

If the wavelength of the electron is so large that it does not fit through the constriction, the electron flux is very low. "When the energy of the electron is increased, its wavelength decreases", explains Libisch. "At some point, one wavelength fits through the constriction, then two wavelengths, then three - this way the electron flux increases in characteristic steps." The electric current is not a continuous quantity, it is quantized.

Theory and Experiment

This effect can also be observed in other materials. Detecting it in graphene was much more difficult, because its complex electronic properties lead to a multitude of additional effects, interfering with each other. The experiments were performed at the group of Christoph Stampfer at the RWTH Aachen (Germany), theoretical calculations and computer simulations were performed in Vienna by Larisa Chizhova and Florian Libisch at the group of Joachim Burgdörfer.

For the experiments, the graphene sheets hat to be etched into shape with nanometre precision. "Protecting the graphene layer by sandwiching it between atomic layers of hexagonal boron nitride is critical for demonstrating the quantized nature of current in graphene" explains Christoph Stampfer. Current through the devices is then measured at extremely low temperatures. "We use liquid helium to cool our samples, otherwise the fragile quantum effects are washed out by thermal fluctuations" says Stampfer. Simulating the experiment poses just as much of a challenge. "A freely moving electron in the graphene sheet can occupy as many quantum states as there are carbon atoms", says Florian Libisch, "more than ten million, in our case." This makes the calculations extremely demanding. An electron in a hydrogen atom can be described using just a few quantum states. The team at TU Wien (Vienna) developed a large scale computer simulation and calculated the behaviour of the electrons in graphene on the Vienna Scientific Cluster VSC, using hundreds of processor cores in parallel.

Edge States

As it turns out, the edge of the graphene sheet plays a crucial role. "As the atoms are arranged in a hexagonal pattern, the edge can never be a completely straight line. On an atomic scale, the edge is always jagged", says Florian Libisch. In these regions, the electrons can occupy special edge states, which have an important influence on the electronic properties of the material. "Only with large scale computer simulations using the most powerful scientific computer clusters available today, we can find out how these edge states affect the electrical current", says Libisch. "The excellent agreement between the experimental results and our theoretical calculations shows that we have been very successful."

The discovery of graphene opened the door to a new research area: ultrathin materials which only consist of very few atomic layers are attracting a lot of attention. Especially the combination of graphene and other materials - such as boron nitride, as in this case - is expected to yield interesting results. "One thing is for sure: whoever wants to understand tomorrow's electronics has to know a lot about quantum physics", says Florian Libisch.

####

For more information, please click here

Contacts:
Florian Aigner

43-158-801-41027

Further information:
Dr. Florian Libisch
Institute for Theoretical Physics
TU Wien
Wiedner Hauptstraße 8-10, 1040 Wien
T: +43-1-58801-13608

Copyright © Vienna University of Technology

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related Links

Original publication: "Size quantization of Dirac fermions in graphene constrictions", Nature Communications, DOI: 10.1038/NCOMMS11528:

Related News Press

News and information

When Dirac meets frustrated magnetism August 3rd, 2020

New printing process advances 3D capabilities: Technology aims to improve quality of products used in business, industry and at home July 31st, 2020

TU Graz researchers synthesize nanoparticles tailored for special applications July 31st, 2020

Scientists discover new class of semiconducting entropy-stabilized materials July 31st, 2020

2 Dimensional Materials

Physicists find misaligned carbon sheets yield unparalleled properties July 31st, 2020

Excitons form superfluid in certain 2D combos: Rice University researchers find ‘paradox’ in ground-state bilayers June 15th, 2020

Transparent graphene electrodes might lead to new generation of solar cells: New roll-to-roll production method could enable lightweight, flexible solar devices and a new generation of display screens June 8th, 2020

Graphene/ Graphite

Physicists find misaligned carbon sheets yield unparalleled properties July 31st, 2020

Graphene-Adsorbate van der Waals bonding memory inspires 'smart' graphene sensors July 17th, 2020

Porous graphene ribbons doped with nitrogen for electronics and quantum computing July 10th, 2020

Quantum Physics

Atomtronic device could probe boundary between quantum, everyday worlds: Clouds of supercooled atoms offer highly sensitive rotation sensors and tests of quantum mechanics July 17th, 2020

Quantum simulation: Particle behavior near the event horizon of block hole July 16th, 2020

Thin films

Extremely low thermal conductivity in 1D soft chain structure BiSeX (X = Br, I) June 19th, 2020

Transparent graphene electrodes might lead to new generation of solar cells: New roll-to-roll production method could enable lightweight, flexible solar devices and a new generation of display screens June 8th, 2020

Possible Futures

Physicists find misaligned carbon sheets yield unparalleled properties July 31st, 2020

Way, shape and form: Synthesis conditions define the nanostructure of manganese dioxide July 31st, 2020

New printing process advances 3D capabilities: Technology aims to improve quality of products used in business, industry and at home July 31st, 2020

Scientists discover new class of semiconducting entropy-stabilized materials July 31st, 2020

Chip Technology

When Dirac meets frustrated magnetism August 3rd, 2020

TU Graz researchers synthesize nanoparticles tailored for special applications July 31st, 2020

Scientists discover new class of semiconducting entropy-stabilized materials July 31st, 2020

Porous graphene ribbons doped with nitrogen for electronics and quantum computing July 10th, 2020

Nanoelectronics

Oriented hexagonal boron nitride foster new type of information carrier May 22nd, 2020

A new strategy to create 2D magnetic order April 10th, 2020

Double-walled nanotubes have electro-optical advantages :Rice University calculations show they could be highly useful for solar panels March 27th, 2020

O-FIB: Far-field-induced near-field breakdown for direct nanowriting in an atmospheric environment March 20th, 2020

Discoveries

When Dirac meets frustrated magnetism August 3rd, 2020

Way, shape and form: Synthesis conditions define the nanostructure of manganese dioxide July 31st, 2020

New printing process advances 3D capabilities: Technology aims to improve quality of products used in business, industry and at home July 31st, 2020

TU Graz researchers synthesize nanoparticles tailored for special applications July 31st, 2020

Materials/Metamaterials

Way, shape and form: Synthesis conditions define the nanostructure of manganese dioxide July 31st, 2020

TU Graz researchers synthesize nanoparticles tailored for special applications July 31st, 2020

Study: Mapping crystal shapes could fast-track 2D materials: Experts call for global effort to clear hurdles to mass production July 27th, 2020

Discovery of disordered nanolayers in intermetallic alloys: Resolving alloys' strength-ductility trade-off and thermal instability July 24th, 2020

Announcements

When Dirac meets frustrated magnetism August 3rd, 2020

New printing process advances 3D capabilities: Technology aims to improve quality of products used in business, industry and at home July 31st, 2020

TU Graz researchers synthesize nanoparticles tailored for special applications July 31st, 2020

Scientists discover new class of semiconducting entropy-stabilized materials July 31st, 2020

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers/Posters

When Dirac meets frustrated magnetism August 3rd, 2020

Way, shape and form: Synthesis conditions define the nanostructure of manganese dioxide July 31st, 2020

New printing process advances 3D capabilities: Technology aims to improve quality of products used in business, industry and at home July 31st, 2020

TU Graz researchers synthesize nanoparticles tailored for special applications July 31st, 2020

Quantum nanoscience

Macroscopic quantum interference in an ultra-pure metal June 26th, 2020

Process for 'two-faced' nanomaterials may aid energy, information tech June 26th, 2020

An EPiQS Pursuit: Physicist Andrea Young is chosen to receive an Experimental Investigator award from the Moore Foundation May 28th, 2020

Scientists break the link between a quantum material's spin and orbital states: The advance opens a path toward a new generation of logic and memory devices based on orbitronics that could be 10,000 times faster than today's May 15th, 2020

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project