Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers Hear Puzzling New Physics from Graphene Quartet's Quantum Harmonies

09.09.2010
Using a one-of-a-kind instrument designed and built at the National Institute of Standards and Technology (NIST), researchers have “unveiled” a quartet of graphene’s electron states and discovered that electrons in graphene can split up into an unexpected and tantalizing set of energy levels when exposed to extremely low temperatures and extremely high magnetic fields.

Published in this week’s issue of Nature,* the new research raises several intriguing questions about the fundamental physics of this exciting material and reveals new effects that may make graphene even more powerful than previously expected for practical applications.

Graphene is one of the simplest materials—a single-atom-thick sheet of carbon atoms arranged in a honeycomb-like lattice—yet it has many remarkable and surprisingly complex properties. Measuring and understanding how electrons carry current through the sheet is important to realizing its technological promise in wide-ranging applications, including high speed electronics and sensors. For example, the electrons in graphene act as if they have no mass and are almost 100 times more mobile than in silicon. Moreover, the speed with which electrons move through graphene is not related to their energy, unlike materials such as silicon where more voltage must be applied to increase their speed, which creates heat that is detrimental to most applications.

To fully understand the behavior of graphene’s electrons, scientists must study the material under an extreme environment of ultra-high vacuum, ultra-low temperatures, and large magnetic fields. Under these conditions, the graphene sheet remains pristine for weeks, and the energy levels and interactions between the electrons can be observed with precision (see "Graphene Yields Secrets to Its Extraordinary Properties," http://www.nist.gov/public_affairs/techbeat/tbx20090514_graphene.htm, NIST Tech Beat Extra, May 14, 2009).

NIST has recently constructed the world’s most powerful and stable scanning-probe microscope, with an unprecedented combination of low temperature (as low as 10 millikelvin, or 10 thousandths of a degree above absolute zero), ultra-high vacuum, and high magnetic field. In the first measurements made with this instrument, the international team has used its power to resolve the finest differences in the electron energies in graphene, atom-by-atom.

“Going to this resolution allows you to see new physics,” said Young Jae Song, a postdoctoral researcher who helped develop the instrument at NIST and make these first measurements.

And the new physics the team saw raises a few more questions about how the electrons behave in graphene than it answers.

Because of the geometry and electromagnetic properties of graphene’s structure, an electron in any given energy level populates four possible sublevels, called a “quartet.” Theorists have predicted that this quartet of levels would split into different energies when immersed in a magnetic field, but until recently there had not been an instrument sensitive enough to resolve these differences.

“When we increased the magnetic field at extreme low temperatures, we observed unexpectedly complex quantum behavior of the electrons,” said NIST Fellow Joseph Stroscio.

What is happening, according to Stroscio, appears to be a “many-body effect” in which electrons interact strongly with one another in ways that affect their energy levels.

One possible explanation for this behavior is that the electrons have formed a “condensate” in which they cease moving independently of one another and act as a single coordinated unit.

“If our hypothesis proves to be correct, it could point the way to the creation of smaller, very-low-heat producing, highly energy efficient electronic devices based upon graphene,” said Shaffique Adam, a postdoctoral researcher who assisted with theoretical analysis of the measurements.

The research team, led by Joseph Stroscio, includes collaborators from NIST, the University of Maryland, Seoul National University, the Georgia Institute of Technology, and the University of Texas at Austin.

The group’s work was also recently featured in Nature Physics,** in which they describe how the energy levels of graphene’s electrons vary with position as they move along the material’s crystal structure. The way in which the energy varies suggests that interactions between electrons in neighboring layers may play a role.

*Y. J. Song, A. F. Otte, Y. Kuk, Y. Hu, D. B. Torrance, P. N. First, W. A. de Heer, H. Min, S. Adam, M. D. Stiles, A. H. MacDonald, and J. A. Stroscio. High Resolution Tunnelling Spectroscopy of a Graphene Quartet, Nature, Sept. 9, 2010.

**D. L. Miller, K. D. Kubista, G. M. Rutter, Ming Ruan, W. A. de Heer, M. Kindermann, P. N. First, and J. A. Stroscio. Real-space mapping of magnetically quantized graphene states. Nature Physics. Published online Aug. 8, 2010. http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys1736.html

Mark Esser | Newswise Science News
Further information:
http://www.nist.gov

More articles from Physics and Astronomy:

nachricht Significantly more productivity in USP lasers
06.12.2016 | Fraunhofer-Institut für Lasertechnik ILT

nachricht Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore

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: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Predicting unpredictability: Information theory offers new way to read ice cores

07.12.2016 | Earth Sciences

Sea ice hit record lows in November

07.12.2016 | Earth Sciences

New material could lead to erasable and rewriteable optical chips

07.12.2016 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>