Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A novel graphene quantum dot structure takes the cake

24.08.2018

In a marriage of quantum science and solid-state physics, researchers at the National Institute of Standards and Technology (NIST) have used magnetic fields to confine groups of electrons to a series of concentric rings within graphene, a single layer of tightly packed carbon atoms.

This tiered "wedding cake," which appears in images that show the energy level structure of the electrons, experimentally confirms how electrons interact in a tightly confined space according to long-untested rules of quantum mechanics. The findings could also have practical applications in quantum computing.


Electrons arranged in a wedding-cake like structure, a concentric series of insulating (red) and conducting (blue) rings, due to magnetic confinement in graphene. The height of each tier represents the energy of the electrons in that tier.

Credit: C. Gutiérrez/NIST

Graphene is a highly promising material for new electronic devices because of its mechanical strength, its excellent ability to conduct electricity and its ultrathin, essentially two-dimensional structure. For these reasons, scientists welcome any new insights on this wonder material.

The researchers, who report their findings in the Aug. 24 issue of Science, began their experiment by creating quantum dots--tiny islands that act as artificial atoms--in graphene devices cooled to just a few degrees above absolute zero.

Electrons orbit quantum dots similar to the way these negatively charged particles orbit atoms. Like rungs on a ladder, they can only occupy specific energy levels according to the rules of quantum theory.

But something special happened when the researchers applied a magnetic field, which further confined the electrons orbiting the quantum dot. When the applied field reached a strength of about 1 Tesla (some 100 times the typical strength of a small bar magnet), the electrons packed closer together and interacted more strongly.

As a result, the electrons rearranged themselves into a novel pattern: an alternating series of conducting and insulating concentric rings on the surface. When the researchers stacked images of the concentric rings recorded at different electron energy levels, the resulting picture resembled a wedding cake, with electron energy as the vertical dimension.

A scanning tunneling microscope, which images surfaces with atomic-scale resolution by recording the flow of electrons between different regions of the sample and the ultrasharp tip of the microscope's stylus, revealed the structure.

"This is a textbook example of a problem--determining what the combined effect of spatial and magnetic confinement of electrons looks like--that you solve on paper when you're first exposed to quantum mechanics, but that no one's actually seen before," said NIST scientist and co-author Joseph Stroscio.

"The key is that graphene is a truly two-dimensional material with an exposed sea of electrons at the surface," he added. "In previous experiments using other materials, quantum dots were buried at material interfaces so no one had been able to look inside them and see how the energy levels change when a magnetic field was applied."

Graphene quantum dots have been proposed as fundamental components of some quantum computers.

"Since we see this behavior begin at moderate fields of just about 1 Tesla, it means that these electron-electron interactions will have to be carefully accounted for when considering certain types of graphene quantum dots for quantum computation," said study co-author Christopher Gutierrez, now at the University of British Columbia in Vancouver, who performed the experimental work at NIST with co-authors Fereshte Ghahari and Daniel Walkup of NIST and the University of Maryland.

This achievement also opens possibilities for graphene to act as what the researchers call a "relativistic quantum simulator." The theory of relativity describes how objects behave when moving at or close to light speed. And electrons in graphene possess an unusual property--they move as if they are massless, like particles of light. Although electrons in graphene actually travel far slower than the speed of light, their light-like massless behavior has earned them the moniker of "relativistic" matter. The new study opens the door to creating a table-top experiment to study strongly confined relativistic matter.

The measurements suggest that scientists may soon find even more exotic structures produced by the interactions of electrons confined to solid-state materials at low temperatures.

###

Collaborators on this work included researchers from the Massachusetts Institute of Technology, Harvard University, the University of Maryland NanoCenter and the National Institute for Material Science in Ibaraki, Japan.

Media Contact

Ben P. Stein
bstein@nist.gov
301-975-2763

 @usnistgov

http://www.nist.gov 

Ben P. Stein | EurekAlert!
Further information:
http://dx.doi.org/10.1126/science.aar2014

More articles from Physics and Astronomy:

nachricht Halfway mark for NOEMA, the super-telescope under construction
20.09.2018 | Max-Planck-Institut für Radioastronomie

nachricht What even Einstein didn't know
20.09.2018 | Technische Universität München

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Scientists present new observations to understand the phase transition in quantum chromodynamics

The building blocks of matter in our universe were formed in the first 10 microseconds of its existence, according to the currently accepted scientific picture. After the Big Bang about 13.7 billion years ago, matter consisted mainly of quarks and gluons, two types of elementary particles whose interactions are governed by quantum chromodynamics (QCD), the theory of strong interaction. In the early universe, these particles moved (nearly) freely in a quark-gluon plasma.

This is a joint press release of University Muenster and Heidelberg as well as the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt.

Then, in a phase transition, they combined and formed hadrons, among them the building blocks of atomic nuclei, protons and neutrons. In the current issue of...

Im Focus: Patented nanostructure for solar cells: Rough optics, smooth surface

Thin-film solar cells made of crystalline silicon are inexpensive and achieve efficiencies of a good 14 percent. However, they could do even better if their shiny surfaces reflected less light. A team led by Prof. Christiane Becker from the Helmholtz-Zentrum Berlin (HZB) has now patented a sophisticated new solution to this problem.

"It is not enough simply to bring more light into the cell," says Christiane Becker. Such surface structures can even ultimately reduce the efficiency by...

Im Focus: New soft coral species discovered in Panama

A study in the journal Bulletin of Marine Science describes a new, blood-red species of octocoral found in Panama. The species in the genus Thesea was discovered in the threatened low-light reef environment on Hannibal Bank, 60 kilometers off mainland Pacific Panama, by researchers at the Smithsonian Tropical Research Institute in Panama (STRI) and the Centro de Investigación en Ciencias del Mar y Limnología (CIMAR) at the University of Costa Rica.

Scientists established the new species, Thesea dalioi, by comparing its physical traits, such as branch thickness and the bright red colony color, with the...

Im Focus: New devices based on rust could reduce excess heat in computers

Physicists explore long-distance information transmission in antiferromagnetic iron oxide

Scientists have succeeded in observing the first long-distance transfer of information in a magnetic group of materials known as antiferromagnets.

Im Focus: Finding Nemo's genes

An international team of researchers has mapped Nemo's genome

An international team of researchers has mapped Nemo's genome, providing the research community with an invaluable resource to decode the response of fish to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

One of the world’s most prominent strategic forums for global health held in Berlin in October 2018

03.09.2018 | Event News

4th Intelligent Materials - European Symposium on Intelligent Materials

27.08.2018 | Event News

LaserForum 2018 deals with 3D production of components

17.08.2018 | Event News

 
Latest News

Fraunhofer ISE with over 60 Contributions at the European PV Solar Energy Conference and Exhibition

21.09.2018 | Trade Fair News

558 million-year-old fat reveals earliest known animal

21.09.2018 | Earth Sciences

Neutrons produce first direct 3D maps of water during cell membrane fusion

21.09.2018 | Health and Medicine

VideoLinks
Science & Research
Overview of more VideoLinks >>>