Featured Research

from universities, journals, and other organizations

Physics Underlying High-Temperature Superconductivity

February 18, 2000
Lawrence Berkeley National Laboratory
Important new insights into the phenomenon known as high-temperature superconductivity have been reported by a team of researchers who used their own customized Scanning Tunneling Microscope (STM) to study the effects of doping a "high-Tc superconductor" with a single "impurity" atom.

Important new insights into the phenomenon known as high-temperature superconductivity have been reported by a team of researchers who used their own customized Scanning Tunneling Microscope (STM) to study the effects of doping a "high-Tc superconductor" with a single "impurity" atom. The research team included scientists with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), the University of California at Berkeley, and the University of Tokyo. Their results are reported in the February 17, 2000 issue of the journal Nature.

The discovery in 1986 of a new class of superconductors -- materials in which electrical resistance drops to zero when cooled below a critical temperature (symbolized as Tc) -- conjured visions of magnetically levitated high-speed trains and dirt-cheap electrical power. Made from ceramic copper oxides rather than the metal alloys of previous superconductors, these new high-Tc superconductors hold promise for superconductivity at room temperatures. For room-temperature materials to ever be realized, however, scientists need a better understanding of the physics behind high-Tc superconductivity.

A key finding in the new report from Berkeley is the first real-space observation of "d-wave symmetry" in a high-Tc superconductor. This is consistent with theoretical models which hold that high-Tc superconductivity involves fluctuations of the magnetic spins of atomic nuclei rather than the phonon-mediated mechanism (vibrations in the atomic lattice) of classical low-Tc superconductors.

"Researchers all over the world have searched for these phenomena for over a decade," says Séamus Davis, who leads the team and holds a joint appointment with Berkeley Lab's Materials Sciences Division and UC Berkeley's Physics Department. "Ours is the first STM study of the effects on high-Tc superconductivity of individual impurity atoms."

In addition to observations consistent with existing theories, Davis and his colleagues also observed phenomena that theorists have not predicted. These surprising observations strongly suggest the need for new and more sophisticated models to explain the physics of high-Tc superconductivity at the atomic scale.

Other authors of the Nature paper, in addition to Davis, were Shuheng Pan (who is now a professor at Boston University), Eric Hudson (now an NRC Fellow at NIST), Kristine Lang of UC Berkeley's Physics Department, and Hiroshi Eisaki and Shin-ichio Uchida of the University of Tokyo's Department of Superconductivity.

The Berkeley researchers worked with a perovskite-type ceramic copper oxide called BSCCO (pronounced bis-ko) because it contains bismuth, strontium, and calcium in addition to copper and oxygen. Like most high-Tc superconductors, BSCCO is a layered material which can be mechanically cleaved to reveal two-dimensional crystal planes that contain only copper and oxygen atoms. In these 2-D copper oxide planes, the researchers had previously substituted single atoms of zinc for single atoms of copper during the crystal-making stage.

High-Tc superconductivity is believed to originate from strongly interacting or "paired" electrons moving through copper oxide layers. A single atom of zinc, a strong scatterer of electrons, substituted for an atom of copper, which would be the source of any paired electrons, proved to be an ideal probe for studying the underlying physics of high-Tc superconductivity.

"Associated with the zinc impurities in the cuprate oxide plane of our samples, we find intense quasi-particle resonances consistent with unitary scattering in a d-wave superconductor," the authors report in their Nature paper. "Density-of-state imaging at the resonance energy shows a highly localized 'quasi-particle cloud' which has a clear four-fold symmetry aligned with the d-wave gap nodes, in qualitative agreement with theory."

Quasi-particles are states of electron excitation that collectively act like a free electron, with energy and angular momentum. D-waves are a function of the angular momentum of the quasi-particles. According to theory, impurity atoms create quasi-particle scattering resonances with characteristic spatial and spectroscopic signatures.

The Berkeley STM images showed intensely bright, cross-shaped, quasi-particle clouds centered directly above the zinc atoms and extending out to about 10 angstroms. These bright crosses are consistent with d-wave symmetry theories which hold that high-Tc superconductivity is mediated by distortions of the magnetic spins in the atomic lattice of the copper oxide layers. The images also validate other theories such as the so-called "Swiss cheese model" which predicts the size and shape of non-superconducting regions around each impurity atom.

"This is the first demonstration of quasi-particle imaging and tunneling spectroscopy at individual impurity atoms in complex materials like the cuprate-oxides," says Davis. "The experimental idea is simple – put one impurity atom at an important site and see what happens – but the technique is so powerful it opens completely new avenues of research including the potential to develop exotic new materials. We've shown that even materials which are structurally and electronically very complex can be studied one atom at a time."

The STM used in this experiment was designed and constructed by Davis and his colleagues Pan and Hudson. Operable at temperatures as low as 0.25 degrees above absolute zero and capable of simultaneously measuring both the surface topography and the density of state of a sample with atomic resolution, this STM is optimized for the study of high-Tc superconducting materials. Images are recorded when the ultra-fine tip of the STM (only a few atoms wide) is passed over a sample about a billionth of a meter (one nanometer) above the surface. An electrical current, generated between the atoms on the sample surface and the STM tip, through which electrons can "tunnel," causes displacements of the tip that can be recorded and translated into topographic images. The STM can also be used to detect physical phenomena such as electrostatic and magnetic forces.

Among the findings by Davis and his colleagues not predicted by theorists was a second cross-shaped quasi-particle cloud, about three times larger but much less bright than the first and rotated about 45-degrees relative to it. More surprises are expected when the Berkeley group replaces copper atoms with impurity atoms other than zinc. Davis' research group has also constructed the first known superconducting tip for an STM. Made from niobium and operable in a powerful magnetic field (7.2 Tesla), this superconducting tip could give Davis and his colleagues the ability to study the magnetic spins of individual atoms which would be a major advance towards unlocking the secrets of high-Tc superconductivity.

"No one knows the precise recipe for making new higher temperature superconductors," says Davis. "To find that recipe it would be tremendously helpful to understand how high-Tc superconductivity works at the atomic level."

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.

Related Links:

* Séamus Davis group Web site -- http://socrates.berkeley.edu/~davisgrp

* UC Berkeley news release -- http://www.urel.berkeley.edu/urel_1/CampusNews/PressReleases/releases/02-16-2000.html

Story Source:

The above story is based on materials provided by Lawrence Berkeley National Laboratory. Note: Materials may be edited for content and length.

Cite This Page:

Lawrence Berkeley National Laboratory. "Physics Underlying High-Temperature Superconductivity." ScienceDaily. ScienceDaily, 18 February 2000. <www.sciencedaily.com/releases/2000/02/000218055054.htm>.
Lawrence Berkeley National Laboratory. (2000, February 18). Physics Underlying High-Temperature Superconductivity. ScienceDaily. Retrieved October 21, 2014 from www.sciencedaily.com/releases/2000/02/000218055054.htm
Lawrence Berkeley National Laboratory. "Physics Underlying High-Temperature Superconductivity." ScienceDaily. www.sciencedaily.com/releases/2000/02/000218055054.htm (accessed October 21, 2014).

Share This

More Matter & Energy News

Tuesday, October 21, 2014

Featured Research

from universities, journals, and other organizations

Featured Videos

from AP, Reuters, AFP, and other news services

Thanks, Marty McFly! Hoverboards Could Be Coming In 2015

Thanks, Marty McFly! Hoverboards Could Be Coming In 2015

Newsy (Oct. 21, 2014) — If you've ever watched "Back to the Future Part II" and wanted to get your hands on a hoverboard, well, you might soon be in luck. Video provided by Newsy
Powered by NewsLook.com
Robots to Fly Planes Where Humans Can't

Robots to Fly Planes Where Humans Can't

Reuters - Innovations Video Online (Oct. 21, 2014) — Researchers in South Korea are developing a robotic pilot that could potentially replace humans in the cockpit. Unlike drones and autopilot programs which are configured for specific aircraft, the robots' humanoid design will allow it to fly any type of plane with no additional sensors. Ben Gruber reports. Video provided by Reuters
Powered by NewsLook.com
Graphene Paint Offers Rust-Free Future

Graphene Paint Offers Rust-Free Future

Reuters - Innovations Video Online (Oct. 21, 2014) — British scientists have developed a prototype graphene paint that can make coatings which are resistant to liquids, gases, and chemicals. The team says the paint could have a variety of uses, from stopping ships rusting to keeping food fresher for longer. Jim Drury reports. Video provided by Reuters
Powered by NewsLook.com
Portable Breathalyzer Gets You Home Safely

Portable Breathalyzer Gets You Home Safely

Buzz60 (Oct. 21, 2014) — Breeze, a portable breathalyzer, gets you home safely by instantly showing your blood alcohol content, and with one tap, lets you call an Uber, a cab or a friend from your contact list to pick you up. Sean Dowling (@SeanDowlingTV) has the details. Video provided by Buzz60
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.


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


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