Nanotechnology Now

Our NanoNews Digest Sponsors





Heifer International

Wikipedia Affiliate Button


android tablet pc

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

East China University of Science and Technology Purchases Nanonex Advanced Nanoimprint Tool NX-B200 July 30th, 2014

Watching Schrödinger's cat die (or come to life): Steering quantum evolution & using probes to conduct continuous error correction in quantum computers July 30th, 2014

From Narrow to Broad July 30th, 2014

FLAG-ERA and TNT2014 join efforts: Graphene Networking at its higher level in Barcelona: Encourage the participation in a joint transnational call July 30th, 2014

Superconductivity

UCF Nanotech Spinout Developing Revolutionary Battery Technology: Power the Next Generation of Electronics with Carbon July 23rd, 2014

Flashes of light on the superconductor: Using light to modulate the properties of a copper-based superconductor July 15th, 2014

Iranian researchers Produce High-Temperature Superconductive Nanorods July 7th, 2014

Bending the rules: A UCSB postdoctoral scholar in physics discovers a counterintuitive phenomenon: the coexistence of superconductivity with dissipation June 29th, 2014

Govt.-Legislation/Regulation/Funding/Policy

New imaging agent provides better picture of the gut July 30th, 2014

Watching Schrödinger's cat die (or come to life): Steering quantum evolution & using probes to conduct continuous error correction in quantum computers July 30th, 2014

Nature inspires a greener way to make colorful plastics July 30th, 2014

Tough foam from tiny sheets: Rice University lab uses atom-thick materials to make ultralight foam July 29th, 2014

Discoveries

New imaging agent provides better picture of the gut July 30th, 2014

Watching Schrödinger's cat die (or come to life): Steering quantum evolution & using probes to conduct continuous error correction in quantum computers July 30th, 2014

From Narrow to Broad July 30th, 2014

A new way to make microstructured surfaces: Method can produce strong, lightweight materials with specific surface properties July 29th, 2014

Announcements

University of Manchester selects Anasys AFM-IR for coatings and corrosion research July 30th, 2014

Nature inspires a greener way to make colorful plastics July 30th, 2014

Analytical solutions from Malvern Instruments support University of Wisconsin-Milwaukee researchers in understanding environmental effects of nanomaterials July 30th, 2014

FEI Unveils New Solutions for Faster Time-to-Analysis in Metals Research July 30th, 2014

Energy

From Narrow to Broad July 30th, 2014

Oregon chemists eye improved thin films with metal substitution: Solution-based inorganic process could drive more efficient electronics and solar devices July 21st, 2014

Steam from the sun: New spongelike structure converts solar energy into steam July 21st, 2014

3-D nanostructure could benefit nanoelectronics, gas storage: Rice U. researchers predict functional advantages of 3-D boron nitride July 15th, 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