Featured Research

from universities, journals, and other organizations

New evidence that magnetism is driving force behind superconductivity

Date:
December 14, 2010
Source:
Rice University
Summary:
Physicists are offering up the strongest evidence yet that magnetism is the driving force behind unconventional superconductivity. Researchers can now describe how collective fluctuations of electrons at the border of magnetism provided more than enough energy to drive superconductivity in recent heavy-fermion experiments.

European and U.S. physicists this week are offering up the strongest evidence yet that magnetism is the driving force behind unconventional superconductivity. The findings by researchers from Rice University, the Max Planck Institute for Chemical Physics of Solids (MPI-CPfS) in Dresden, Germany, and other institutions were published online December 13 in Nature Physics.

The findings follow more than three decades of research by the team that discovered unconventional superconductivity in 1979. That breakthrough, which was led by MPI-CPfS Director Frank Steglich, preceded by seven years the more widely publicized discovery of unconventional superconductivity at high temperatures. In the latest study, the team revisited the same heavy-fermion material -- a mix of cerium, copper and silicon -- that was used in 1979, applying new experimental techniques and theoretical knowledge unavailable 30 years ago.

"In 1979, there was not much understanding of quantum criticality or of the collective way that electrons behave at the border of magnetism," said Rice physicist Qimiao Si, the lead theorist and co-author of the new paper. "Today, we know a great deal about such collective behavior in the regime where materials transition to a superconducting state. The question we examined in this study is, How does all of that new knowledge translate into an understanding of the superconducting state itself?"

Magnetism -- the phenomenon that drives compass needles and keeps notes stuck to refrigerators the world over -- arises when the electrons in a material are oriented in a particular way. Every electron is imbued with a property called spin, and electron spins are oriented either up or down. In most materials, the arrangement of electron spins is haphazard, but in everyday refrigerator magnets -- which scientists call ferromagnets -- electron spins are oriented collectively, in the same direction.

Classical superconductors, which were discovered almost a century ago, were the first materials known to conduct electrons without losing energy due to resistance. Electrons typically bump and ricochet from atom to atom as they travel down a wire, and this jostling leads to a loss of energy in the form of electrical resistance. Resistance costs the energy industry billions of dollars per year in lost power, so scientists have been keen to put superconducting wires to widespread use, but it hasn't been easy.

It took physicists almost 50 years to explain classical superconductivity: At extremely low temperatures, electrons pair up and move in unison, thus avoiding the jostling they experience by themselves. These electron twosomes are called Cooper pairs, and physicists began trying to explain how they form in unconventional superconductors as soon as Steglich's findings were published in 1979. Si said theorists studying the question have increasingly been drawn to the collective behavior of electrons, particularly at the border of magnetism -- the critical point where a material changes from one magnetic state to another.

In the new experiments, Steglich, the lead experimentalist co-author, and his group collaborated with physicists at the Jόlich Centre for Neutron Science at the Institut Laue-Langevin in Grenoble, France, to bombard heavy fermion samples with neutrons. Because neutrons also have spin, those experiments allowed the team to probe the spin states of the electrons in the heavy fermions.

"Our neutron-scattering data provide convincing evidence that the cerium-based heavy fermion compound is located near a quantum critical point," said Oliver Stockert, a study co-author and a neutron-scattering specialist from MPI-CPfS. "Moreover, the data revealed how the magnetic spectrum changes as the material turns into a superconductor."

From the data, Si and co-author Stefan Kirchner, a theorist from the Max Planck Institute for the Physics of Complex Systems and a former postdoctoral fellow at Rice, determined the amount of magnetic energy that was saved when the system entered the superconducting state.

"We have calculated that the saved magnetic energy is more than 10 times what is needed for the formation of the Cooper pairs," Kirchner said.

"Why the magnetic exchange in the superconductor yields such a large energy saving is a new and intriguing question," said Si, Rice's Harry C. and Olga K. Wiess Professor of Physics and Astronomy. He said one possible origin is the electronic phenomenon known as the "Kondo effect," which is involved in a class of unconventional quantum critical points advanced by Si and colleagues in a theoretical paper published in Nature in 2001. Regardless of the final answer, Si said the present study already constitutes a definitive proof that "collective fluctuations of the electrons at the border of magnetism are capable of driving superconductivity."

Si and Steglich found it remarkable that the notion of quantum criticality is providing fresh insights into the workings of the very first unconventional superconductor ever discovered. At the same time, both said more studies are needed to determine the precise way that quantum-critical fluctuations give rise to heavy-fermion superconductivity. And thanks to key differences between the heavy-fermion materials and high-temperature superconductors, additional work must be done to determine whether the same findings apply to both.

"We are certain that we are on the right track with our investigations, however," Steglich said.

The research was facilitated by the International Collaborative Center on Quantum Matter, a collaborative entity formed by Rice, MPI-CPfS, China's Zhejiang University and the London Centre for Nanotechnology. Research support was provided by the German Research Foundation, the National Science Foundation and the Welch Foundation.


Story Source:

The above story is based on materials provided by Rice University. Note: Materials may be edited for content and length.


Journal Reference:

  1. O. Stockert, J. Arndt, E. Faulhaber, C. Geibel, H. S. Jeevan, S. Kirchner, M. Loewenhaupt, K. Schmalzl, W. Schmidt, Q. Si, F. Steglich. Magnetically driven superconductivity in CeCu2Si2. Nature Physics, 2010; DOI: 10.1038/nphys1852

Cite This Page:

Rice University. "New evidence that magnetism is driving force behind superconductivity." ScienceDaily. ScienceDaily, 14 December 2010. <www.sciencedaily.com/releases/2010/12/101213121751.htm>.
Rice University. (2010, December 14). New evidence that magnetism is driving force behind superconductivity. ScienceDaily. Retrieved July 23, 2014 from www.sciencedaily.com/releases/2010/12/101213121751.htm
Rice University. "New evidence that magnetism is driving force behind superconductivity." ScienceDaily. www.sciencedaily.com/releases/2010/12/101213121751.htm (accessed July 23, 2014).

Share This




More Matter & Energy News

Wednesday, July 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Government Approves East Coast Oil Exploration

Government Approves East Coast Oil Exploration

AP (July 18, 2014) — The Obama administration approved the use of sonic cannons to discover deposits under the ocean floor by shooting sound waves 100 times louder than a jet engine through waters shared by endangered whales and turtles. (July 18) Video provided by AP
Powered by NewsLook.com
Sunken German U-Boat Clearly Visible For First Time

Sunken German U-Boat Clearly Visible For First Time

Newsy (July 18, 2014) — The wreckage of the German submarine U-166 has become clearly visible for the first time since it was discovered in 2001. Video provided by Newsy
Powered by NewsLook.com
Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Reuters - US Online Video (July 17, 2014) — President Barak Obama stopped by at a lunch counter in Delaware before making remarks about boosting the nation's infrastructure. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com
Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

TheStreet (July 16, 2014) — Oil Futures are bouncing back after tumbling below $100 a barrel for the first time since May yesterday. Jeff Grossman is the president of BRG Brokerage and trades at the NYMEX. Grossman tells TheStreet the Middle East is always a concern for oil traders. Oil prices were pushed down in recent weeks on Libya increasing its production. Supply disruptions in Iraq fading also contributed to prices falling. News from China's economic front showing a growth for the second quarter also calmed fears on its slowdown. Jeff Grossman talks to TheStreet's Susannah Lee on this and more on the Energy Department's Energy Information Administration (EIA) report. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins