Featured Research

from universities, journals, and other organizations

Point-contact Spectroscopy Deepens Mystery Of Heavy-fermion Superconductors

Date:
April 14, 2005
Source:
University Of Illinois At Urbana-Champaign
Summary:
Theoretical understanding of heavy-fermion superconductors has just slipped a notch or two, says a team of experimentalists. Researchers from the University of Illinois at Urbana-Champaign and Los Alamos National Laboratory recently used a sensitive technique called point-contact spectroscopy to explore Andreev reflection between a normal metal and a heavy-fermion superconductor.

Laura Greene, a Swanlund Endowed Chair in physics at Illinois, and colleagues at Los Alamos National Laboratory recently used a sensitive technique called point-contact spectroscopy to explore Andreev reflection between a normal metal and a heavy-fermion superconductor.
Credit: Photo by Kwame Ross

CHAMPAIGN, Ill. — Theoretical understanding of heavy-fermion superconductors has just slipped a notch or two, says a team of experimentalists.

Researchers from the University of Illinois at Urbana-Champaign and Los Alamos National Laboratory recently used a sensitive technique called point-contact spectroscopy to explore Andreev reflection between a normal metal and a heavy-fermion superconductor. Conventional theories cannot account for their data, the scientists report.

“According to conventional theories, the Fermi velocity mismatch between a normal metal and a heavy-fermion superconductor is too large for Andreev reflection to occur,” said Laura Greene, a Swanlund Endowed Chair in physics at Illinois. “But we can clearly and reproducibly measure it as a matter of course.”

Andreev reflection is a particle-hole conversion process that occurs at the interface of a normal metal and a superconductor. Using point-contact spectroscopy, Greene and postdoctoral research associate Wan Kyu Park obtained measurements of Andreev reflection at the interface of a normal metal (gold) and the heavy-fermion superconductor CeCoIn5 (cerium-cobalt-indium-five).

Andreev reflection can be better understood by drawing an analogy to light, Greene said. When light is incident on glass, some of the light is reflected due to the difference in index of refraction between air and glass, and some is transmitted into the glass. The index of refraction is essentially the velocity difference: light travels slower in glass than in air.

Shining light on a diamond, which has an index of refraction larger than glass, causes more light to be reflected (one of the reasons diamonds appear to glow). The larger the velocity mismatch, the more light will be reflected.

Similarly, when a metal and a superconductor are in good electrical contact and have different Fermi velocities (the speed of electrons at the Fermi energy), some of the electrons will be reflected in a normal fashion. The larger the mismatch, the more electrons will be reflected and the less transmitted.

The Andreev reflection process requires at least some penetration of the electrons into the superconductor, Greene said. If the Fermi velocities are quite disparate, then there is a large fraction of normal reflection and less of a chance for Andreev reflection.

Conventional theory dictated that all of the reflection between a normal metal and a heavy-fermion superconductor would be normal and there would be no Andreev reflection.

“Our measurements prove that existing theories can’t account for Andreev reflection between normal metals and heavy-fermion superconductors,” said Greene, who will present the team’s findings at the spring meeting of the American Physical Society, to be held in Los Angeles, March 21-25.

“The bottom line is, we can understand Andreev reflection occurring between a normal metal and a superconductor, but we can’t understand it occurring between a normal metal and a heavy-fermion superconductor,” Greene said. “We need a whole new theoretical formulation to explain this phenomenon.”

In addition to Greene and Park, the research team included physicists John Sarrao and Joe Thompson at Los Alamos. Tony Leggett (Macarthur Professor of Physics at Illinois), his graduate student, Vladimir Lukic, and an undergraduate student in Greene’s group, Justin Elenewski, are collaborating on this experimental effort in investigating new theoretical frameworks to account for these results. The U.S. Department of Energy funded the work.


Story Source:

The above story is based on materials provided by University Of Illinois At Urbana-Champaign. Note: Materials may be edited for content and length.


Cite This Page:

University Of Illinois At Urbana-Champaign. "Point-contact Spectroscopy Deepens Mystery Of Heavy-fermion Superconductors." ScienceDaily. ScienceDaily, 14 April 2005. <www.sciencedaily.com/releases/2005/03/050325160419.htm>.
University Of Illinois At Urbana-Champaign. (2005, April 14). Point-contact Spectroscopy Deepens Mystery Of Heavy-fermion Superconductors. ScienceDaily. Retrieved October 2, 2014 from www.sciencedaily.com/releases/2005/03/050325160419.htm
University Of Illinois At Urbana-Champaign. "Point-contact Spectroscopy Deepens Mystery Of Heavy-fermion Superconductors." ScienceDaily. www.sciencedaily.com/releases/2005/03/050325160419.htm (accessed October 2, 2014).

Share This



More Matter & Energy News

Thursday, October 2, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Japan Looks To Faster Future As Bullet Train Turns 50

Japan Looks To Faster Future As Bullet Train Turns 50

Newsy (Oct. 1, 2014) Japan's bullet train turns 50 Wednesday. Here's a look at how it's changed over half a century — and the changes it's inspired globally. Video provided by Newsy
Powered by NewsLook.com
US Police Put Body Cameras to the Test

US Police Put Body Cameras to the Test

AFP (Oct. 1, 2014) Police body cameras are gradually being rolled out across the US, with interest surging after the fatal police shooting in August of an unarmed black teenager. Duration: 02:18 Video provided by AFP
Powered by NewsLook.com
Raw: Japan Celebrates 'bullet Train' Anniversary

Raw: Japan Celebrates 'bullet Train' Anniversary

AP (Oct. 1, 2014) A ceremony marking 50 years since Japan launched its Shinkansen bullet train was held on Wednesday in Tokyo. The latest model can travel from Tokyo to Osaka, a distance of 319 miles, in two hours and 25 minutes. (Oct. 1) Video provided by AP
Powered by NewsLook.com
Robotic Hair Restoration

Robotic Hair Restoration

Ivanhoe (Oct. 1, 2014) A new robotic procedure is changing the way we transplant hair. The ARTAS robot leaves no linear scarring and provides more natural results. Video provided by Ivanhoe
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:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

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