Nanotechnology Now

Our NanoNews Digest Sponsors



Heifer International

Wikipedia Affiliate Button


android tablet pc

Home > Press > Long Predicted Atomic Collapse State Observed in Graphene: Berkeley Lab researchers recreate elusive phenomenon with artificial nuclei

An artificial atomic nucleus made up of five charged calcium dimers is centered in an atomic-collapse electron cloud. (Image courtesy of Michael Crommie)
An artificial atomic nucleus made up of five charged calcium dimers is centered in an atomic-collapse electron cloud.

(Image courtesy of Michael Crommie)

Abstract:
The first experimental observation of a quantum mechanical phenomenon that was predicted nearly 70 years ago holds important implications for the future of graphene-based electronic devices. Working with microscopic artificial atomic nuclei fabricated on graphene, a collaboration of researchers led by scientists with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have imaged the "atomic collapse" states theorized to occur around super-large atomic nuclei.

Long Predicted Atomic Collapse State Observed in Graphene: Berkeley Lab researchers recreate elusive phenomenon with artificial nuclei

Berkeley, CA | Posted on March 13th, 2013

"Atomic collapse is one of the holy grails of graphene research, as well as a holy grail of atomic and nuclear physics," says Michael Crommie, a physicist who holds joint appointments with Berkeley Lab's Materials Sciences Division and UC Berkeley's Physics Department. "While this work represents a very nice confirmation of basic relativistic quantum mechanics predictions made many decades ago, it is also highly relevant for future nanoscale devices where electrical charge is concentrated into very small areas."

Crommie is the corresponding author of a paper describing this work in the journal Science. The paper is titled "Observing Atomic Collapse Resonances in Artificial Nuclei on Graphene." Co-authors are Yang Wang, Dillon Wong, Andrey Shytov, Victor Brar, Sangkook Choi, Qiong Wu, Hsin-Zon Tsai, William Regan, Alex Zettl, Roland Kawakami, Steven Louie, and Leonid Levitov.

Originating from the ideas of quantum mechanics pioneer Paul Dirac, atomic collapse theory holds that when the positive electrical charge of a super-heavy atomic nucleus surpasses a critical threshold, the resulting strong Coulomb field causes a negatively charged electron to populate a state where the electron spirals down to the nucleus and then spirals away again, emitting a positron (a positively-charged electron) in the process. This highly unusual electronic state is a significant departure from what happens in a typical atom, where electrons occupy stable circular orbits around the nucleus.

"Nuclear physicists have tried to observe atomic collapse for many decades, but they never unambiguously saw the effect because it is so hard to make and maintain the necessary super-large nuclei," Crommie says. "Graphene has given us the opportunity to see a condensed matter analog of this behavior, since the extraordinary relativistic nature of electrons in graphene yields a much smaller nuclear charge threshold for creating the special supercritical nuclei that will exhibit atomic collapse behavior."

Perhaps no other material is currently generating as much excitement for new electronic technologies as graphene, sheets of pure carbon just one atom thick through which electrons can freely race 100 times faster than they move through silicon. Electrons moving through graphene's two-dimensional layer of carbon atoms, which are arranged in a hexagonally patterned honeycomb lattice, perfectly mimic the behavior of highly relativistic charged particles with no mass. Superthin, superstrong, superflexible, and superfast as an electrical conductor, graphene has been touted as a potential wonder material for a host of electronic applications, starting with ultrafast transistors.

In recent years scientists predicted that highly-charged impurities in graphene should exhibit a unique electronic resonance - a build-up of electrons partially localized in space and energy - corresponding to the atomic collapse state of super-large atomic nuclei. Last summer Crommie's team set the stage for experimentally verifying this prediction by confirming that graphene's electrons in the vicinity of charged atoms follow the rules of relativistic quantum mechanics. However, the charge on the atoms in that study was not yet large enough to see the elusive atomic collapse.

"Those results, however, were encouraging and indicated that we should be able to see the same atomic physics with highly charged impurities in graphene as the atomic collapse physics predicted for isolated atoms with highly charged nuclei," Crommie says. "That is to say, we should see an electron exhibiting a semiclassical inward spiral trajectory and a novel quantum mechanical state that is partially electron-like near the nucleus and partially hole-like far from the nucleus. For graphene we talk about ‘holes' instead of the positrons discussed by nuclear physicists."

To test this idea, Crommie and his research group used a specially equipped scanning tunneling microscope (STM) in ultra-high vacuum to construct, via atomic manipulation, artificial nuclei on the surface of a gated graphene device. The "nuclei" were actually clusters made up of pairs, or dimers, of calcium ions. With the STM, the researchers pushed calcium dimers together into a cluster, one by one, until the total charge in the cluster became supercritical. STM spectroscopy was then used to measure the spatial and energetic characteristics of the resulting atomic collapse electronic state around the supercritical impurity.

"The positively charged calcium dimers at the surface of graphene in our artificial nuclei played the same role that protons play in regular atomic nuclei," Crommie says. "By squeezing enough positive charge into a sufficiently small area, we were able to directly image how electrons behave around a nucleus as the nuclear charge is methodically increased from below the supercritical charge limit, where there is no atomic collapse, to above the supercritical charge limit, where atomic collapse occurs."

Observing atomic collapse physics in a condensed matter system is very different from observing it in a particle collider, Crommie says. Whereas in a particle collider the "smoking gun" evidence of atomic collapse is the emission of a positron from the supercritical nucleus, in a condensed matter system the smoking gun is the onset of a signature electronic state in the region nearby the supercritical nucleus. Crommie and his group observed this signature electronic state with artificial nuclei of three or more calcium dimers.

"The way in which we observe the atomic collapse state in condensed matter and think about it is quite different from how the nuclear and high-energy physicists think about it and how they have tried to observe it, but the heart of the physics is essentially the same," says Crommie.

If the immense promise of graphene-based electronic devices is to be fully realized, scientists and engineers will need to achieve a better understanding of phenomena such as this that involve the interactions of electrons with each other and with impurities in the material.

"Just as donor and acceptor states play a crucial role in understanding the behavior of conventional semiconductors, so too should atomic collapse states play a similar role in understanding the properties of defects and dopants in future graphene devices," Crommie says. "Because atomic collapse states are the most highly localized electronic states possible in pristine graphene, they also present completely new opportunities for directly exploring and understanding electronic behavior in graphene."

In addition to Berkeley Lab and UC Berkeley, other institutions represented in this work include UC Riverside, MIT, and the University of Exeter.

Berkeley Lab's work was supported by DOE's Office of Science. Other members of the research team received support from the Office of Naval Research and the National Science Foundation. Computational resources were provided by DOE at Berkeley Lab's NERSC facility.

####

About Berkeley Lab
Lawrence Berkeley National Laboratory (Berkeley Lab) addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov.

For more information, please click here

Contacts:
Lynn Yarris
(510) 486-5375

Copyright © Berkeley

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

For more about the research of Michael Crommie, go here:

Related News Press

News and information

Wear-resistant ceramic powder maximises component lifespan in high-stress applications: Innovnano’s nanostructured 3YSZ offers improved tribological performance for manufacturing components September 18th, 2014

IEEE International Electron Devices Meeting To Celebrate 60th Anniversary as The Leading Technical Conference for Advanced Semiconductor Devices September 18th, 2014

FEI Opens New Technology Center in Czech Republic: FEI expands its presence in Brno with the opening of a new, larger facility September 18th, 2014

Biosensors Get a Boost from Graphene Partnership: $5 Million Investment Supports Dozens of Jobs and Development of 300mm Fabrication Process and Wafer Transfer Facility September 18th, 2014

The Pocket Project will develop a low-cost and accurate point-of-care test to diagnose Tuberculosis: ICN2 holds a follow-up meeting of the Project on September 18th - 19th September 18th, 2014

Imaging

IEEE International Electron Devices Meeting To Celebrate 60th Anniversary as The Leading Technical Conference for Advanced Semiconductor Devices September 18th, 2014

FEI Opens New Technology Center in Czech Republic: FEI expands its presence in Brno with the opening of a new, larger facility September 18th, 2014

New NPZ100-403 Piezo Stage from nPoint Inc. September 17th, 2014

Graphene

Biosensors Get a Boost from Graphene Partnership: $5 Million Investment Supports Dozens of Jobs and Development of 300mm Fabrication Process and Wafer Transfer Facility September 18th, 2014

New pricing report for bulk graphene materials September 13th, 2014

Laboratories

Elusive Quantum Transformations Found Near Absolute Zero: Brookhaven Lab and Stony Brook University researchers measured the quantum fluctuations behind a novel magnetic material's ultra-cold ferromagnetic phase transition September 15th, 2014

'Squid skin' metamaterials project yields vivid color display: Rice lab creates RGB color display technology with aluminum nanorods September 15th, 2014

Berkeley Lab Licenses Boron Nitride Nanotube Technology: New material has unique mechanical and electronic properties September 13th, 2014

Physics

Elusive Quantum Transformations Found Near Absolute Zero: Brookhaven Lab and Stony Brook University researchers measured the quantum fluctuations behind a novel magnetic material's ultra-cold ferromagnetic phase transition September 15th, 2014

Govt.-Legislation/Regulation/Funding/Policy

Scientists refine formula for nanotube types: Rice University theorists determine factors that give tubes their chiral angles September 17th, 2014

New non-invasive technique could revolutionize the imaging of metastatic cancer September 17th, 2014

Recruiting bacteria to be technology innovation partners: September 17th, 2014

Nanoribbon film keeps glass ice-free: Rice University lab refines deicing film that allows radio frequencies to pass September 16th, 2014

Chip Technology

IEEE International Electron Devices Meeting To Celebrate 60th Anniversary as The Leading Technical Conference for Advanced Semiconductor Devices September 18th, 2014

‘Small’ transformation yields big changes September 16th, 2014

Excitonic Dark States Shed Light on TMDC Atomic Layers: Berkeley Lab Discovery Holds Promise for Nanoelectronic and Photonic Applications September 11th, 2014

Researchers Create World’s Largest DNA Origami September 11th, 2014

Discoveries

The Pocket Project will develop a low-cost and accurate point-of-care test to diagnose Tuberculosis: ICN2 holds a follow-up meeting of the Project on September 18th - 19th September 18th, 2014

New non-invasive technique could revolutionize the imaging of metastatic cancer September 17th, 2014

Toward making lithium-sulfur batteries a commercial reality for a bigger energy punch September 17th, 2014

Recruiting bacteria to be technology innovation partners: September 17th, 2014

Materials/Metamaterials

Wear-resistant ceramic powder maximises component lifespan in high-stress applications: Innovnano’s nanostructured 3YSZ offers improved tribological performance for manufacturing components September 18th, 2014

Next-Gen Luxury RV From Global Caravan Technologies Will Offer MagicView Roof and Windshield Using SPD-SmartGlass Technology From Research Frontiers: Recreational Vehicle Manufacturer Global Caravan Technologies (GCT) Features 28 Square Feet of MagicView™ SPD-SmartGlass September 17th, 2014

Nanoribbon film keeps glass ice-free: Rice University lab refines deicing film that allows radio frequencies to pass September 16th, 2014

‘Small’ transformation yields big changes September 16th, 2014

Announcements

Wear-resistant ceramic powder maximises component lifespan in high-stress applications: Innovnano’s nanostructured 3YSZ offers improved tribological performance for manufacturing components September 18th, 2014

IEEE International Electron Devices Meeting To Celebrate 60th Anniversary as The Leading Technical Conference for Advanced Semiconductor Devices September 18th, 2014

FEI Opens New Technology Center in Czech Republic: FEI expands its presence in Brno with the opening of a new, larger facility September 18th, 2014

Biosensors Get a Boost from Graphene Partnership: $5 Million Investment Supports Dozens of Jobs and Development of 300mm Fabrication Process and Wafer Transfer Facility September 18th, 2014

Tools

IEEE International Electron Devices Meeting To Celebrate 60th Anniversary as The Leading Technical Conference for Advanced Semiconductor Devices September 18th, 2014

FEI Opens New Technology Center in Czech Republic: FEI expands its presence in Brno with the opening of a new, larger facility September 18th, 2014

New NPZ100-403 Piezo Stage from nPoint Inc. September 17th, 2014

Researchers Create World’s Largest DNA Origami September 11th, 2014

Military

Scientists refine formula for nanotube types: Rice University theorists determine factors that give tubes their chiral angles September 17th, 2014

Nanoribbon film keeps glass ice-free: Rice University lab refines deicing film that allows radio frequencies to pass September 16th, 2014

'Squid skin' metamaterials project yields vivid color display: Rice lab creates RGB color display technology with aluminum nanorods September 15th, 2014

Fonon at Cutting-Edge of 3D Military Printing: Live-Combat Scenarios Could See a Decisive Advantage with 3D Printing September 15th, 2014

Energy

IEEE International Electron Devices Meeting To Celebrate 60th Anniversary as The Leading Technical Conference for Advanced Semiconductor Devices September 18th, 2014

Rice rolls 'neat' nanotube fibers: Rice University researchers' acid-free approach leads to strong conductive carbon threads September 15th, 2014

Simple, Cost-Effective Method Proposed for Synthesizing Zinc Oxide Nanopigments September 15th, 2014

UT Arlington research uses nanotechnology to help cool electrons with no external sources September 11th, 2014

Research partnerships

Biosensors Get a Boost from Graphene Partnership: $5 Million Investment Supports Dozens of Jobs and Development of 300mm Fabrication Process and Wafer Transfer Facility September 18th, 2014

The Pocket Project will develop a low-cost and accurate point-of-care test to diagnose Tuberculosis: ICN2 holds a follow-up meeting of the Project on September 18th - 19th September 18th, 2014

Recruiting bacteria to be technology innovation partners: September 17th, 2014

Carbon Sciences Developing Breakthrough Technology to Mass-Produce Graphene -- the New Miracle Material: Company Enters Into an Agreement With the University of California, Santa Barbara (UCSB) to Fund the Further Development of a New Graphene Process September 16th, 2014

Quantum nanoscience

Elusive Quantum Transformations Found Near Absolute Zero: Brookhaven Lab and Stony Brook University researchers measured the quantum fluctuations behind a novel magnetic material's ultra-cold ferromagnetic phase transition September 15th, 2014

Layered graphene sandwich for next generation electronics September 8th, 2014

Cool Calculations for Cold Atoms: New theory of universal three-body encounters September 2nd, 2014

New technique uses fraction of measurements to efficiently find quantum wave functions August 28th, 2014

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



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More














ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







© Copyright 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE