Nanotechnology Now





Heifer International

Wikipedia Affiliate Button


DHgate

Home > Press > A theory linking two 'broken symmetries' in high-temperature superconductors is proposed and verified

Simulations, left, of where theory predicts that "singularities" should appear in two small sections of a cuprate superconductor, and STM measurements, right, of where they actually appear.
Simulations, left, of where theory predicts that "singularities" should appear in two small sections of a cuprate superconductor, and STM measurements, right, of where they actually appear.

Abstract:
A theory advanced by a Cornell theoretical physicist to link two "broken symmetries" in a high-temperature superconductor has been verified by experiment, bringing scientists a step closer to understanding and perhaps improving superconducting materials.

A theory linking two 'broken symmetries' in high-temperature superconductors is proposed and verified

Ithaca, NY | Posted on July 21st, 2011

"Such agreement between theory and experiment is rare since high--temperature superconductivity in cuprates has evaded scientists' understanding for over two decades," said Eun-Ah Kim, assistant professor of physics. "Many models have been proposed, but because this one has been verified by experiment it gives us a jumping-off place for further work."

The results are reported in the July 22 issue of the journal Science with Kim as senior author. The work is a followup to the researchers' previous discovery of a broken symmetry in cuprate bonds reported in the July 15, 2010, issue of Nature.

Under certain conditions, observations with a highly sensitive scanning tunneling microscope (STM) show an anomaly in the distribution of energy levels of the electrons bonding copper and oxygen atoms in a cuprate crystal. There also may be interruptions in the orderly wavelike distribution of those energy levels across the entire crystal. Kim proposed an equation to link the two phenomena.

Simulations based on Kim's theory agree closely with STM observations of a cuprate superconductor containing bismuth, strontium and calcium by co-author J. C. Séamus Davis, the James Gilbert White Distinguished Professor in the Physical Sciences at Cornell. "The notion of symmetry can offer a powerful organizing principle for understanding in physics, if you know which symmetries to focus on," Kim said. "Building on our previous work, we zoomed into two particular broken symmetries."

Superconductivity, where a current flows with zero resistance, was first discovered in metals cooled close to absolute zero (-273 degrees Celsius). Cuprates, made up of copper oxide layers alternating with layers of other "dopant" elements, superconduct at temperatures as "high" as 150 degrees above absolute zero.

An STM uses a probe so tiny that its tip is a single atom, scanned across a surface in steps smaller than the width of an atom. By measuring the current flow between the tip and a surface, Davis can identify the "energy states" of electrons under the probe, which can be thought of as the amount of energy needed to pull an electron loose from its atom. A characteristic of high-temperature superconductors is that certain energy states are missing, and it's believed the missing electrons have gone to form so-called "Cooper pairs" that can move without resistance.

At temperatures above the superconducting transition temperature, cuprates still show this "energy gap," but no longer superconduct. In some materials this "pseudogap" is found all the way up to room temperature, so understanding how it works could show how to design new materials that would superconduct at higher temperatures.

STM images show that in the pseudogap condition the number of electron states varies in a wavelike pattern across a cuprate crystal, so a graph of them looks like ridges in corduroy. But here and there the symmetry of this pattern is broken by what Kim calls singularities, where, for example, one stripe splits into two. Mathematically, these are points where the number of electron states winds up to a peak like a little whirlpool.

More recently, the team found that in the checkerboard arrangement of copper and oxygen in a cuprate, the density of electron energy states between the copper and oxygen atoms is different looking "north and south" than "east and west" -- how much different varies from place to place across the crystal. Kim's theory now predicts that this variation is coupled to the singularities. Singularities should occur at places where the north-south/east-west difference equals the average of such differences across the entire crystal, and STM measurements agree with the prediction. "We have applied this to many sets of data going back almost a decade," Kim said.

The next step, she said, is to see how these locations relate to the arrangement of doping atoms in the crystal layers between copper oxide sheets. That alone may not give us room-temperature superconductors, but it could reveal more about how the pseudogap works.

"Is the pseudogap a preparation for superconductivity or is it inhibiting?" Kim asked. "This development allows us to quantify the degree of broken symmetry and may help answer the question."

The research was supported in part by the National Science Foundation and the U.S. Department of Energy.

####

For more information, please click here

Contacts:
Media Contact:
Blaine Friedlander
(607) 254-8093


Cornell Chronicle:
Bill Steele
(607) 255-7164

Copyright © Cornell University

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 News Press

News and information

Conversion of Greenhouse Gases to Syngas in Presence of Nanocatalysts in Iran May 22nd, 2015

New Antibacterial Wound Dressing in Iran Can Display Replacement Time May 22nd, 2015

Haydale Named Lead Sponsor for Cambridge Graphene Festival May 22nd, 2015

Simulations predict flat liquid May 21st, 2015

Superconductivity

Science and Technology of Advanced Materials (STAM): Reported successes and failures aid hot pursuit of superconductivity May 15th, 2015

Researchers discover 'swing-dancing' pairs of electrons: Findings set the stage for room-temperature superconductivity and the transformation of high-speed rail, quantum computers May 14th, 2015

Oxford Instruments announces winners of the 2015 Sir Martin Wood Science Prize for China May 2nd, 2015

Novel superconducting undulator provides first x-ray light at ANKA May 1st, 2015

Govt.-Legislation/Regulation/Funding/Policy

Nanotherapy effective in mice with multiple myeloma May 21st, 2015

Turn that defect upside down: Twin boundaries in lithium-ion batteries May 21st, 2015

INSIDDE: Uncovering the real history of art using a graphene scanner May 21st, 2015

SUNY Poly CNSE and NIOSH Launch Federal Nano Health and Safety Consortium: May 20th, 2015

Discoveries

Conversion of Greenhouse Gases to Syngas in Presence of Nanocatalysts in Iran May 22nd, 2015

New Antibacterial Wound Dressing in Iran Can Display Replacement Time May 22nd, 2015

Nanotherapy effective in mice with multiple myeloma May 21st, 2015

Turn that defect upside down: Twin boundaries in lithium-ion batteries May 21st, 2015

Announcements

Conversion of Greenhouse Gases to Syngas in Presence of Nanocatalysts in Iran May 22nd, 2015

New Antibacterial Wound Dressing in Iran Can Display Replacement Time May 22nd, 2015

Haydale Named Lead Sponsor for Cambridge Graphene Festival May 22nd, 2015

INSIDDE: Uncovering the real history of art using a graphene scanner May 21st, 2015

Energy

Conversion of Greenhouse Gases to Syngas in Presence of Nanocatalysts in Iran May 22nd, 2015

Sandia researchers first to measure thermoelectric behavior by 'Tinkertoy' materials May 20th, 2015

Industrial Nanotech, Inc. Announces Official Launch of the Eagle Platinum Tile™ May 19th, 2015

FEI and Weatherford Enter Into Joint Agreement for Advanced Reservoir Characterization Services May 18th, 2015

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