Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Copper-oxide plane at surface of superconductor has surprising properties

27.08.2002


The peculiar behavior of high-temperature superconductors has baffled scientists for many years. Now, by imaging the copper-oxide plane in a cuprate superconductor for the first time, researchers at the University of Illinois at Urbana-Champaign have found several new pieces to this important puzzle.

As reported in the Aug. 19 issue of Physical Review Letters, physics professor Ali Yazdani, graduate student Shashank Misra, and colleagues used a scanning tunneling microscope to demonstrate that a single copper-oxide plane can form a stable layer at the superconductor’s surface. This plane behaves differently when exposed at the surface than when buried inside the crystal, the researchers discovered, offering additional insight into the behavior of high-temperature superconductors.

"In contrast to previous studies, we found that this copper-oxide layer exhibits an unusual suppression of tunneling conductance at low energies," Yazdani said. "We think the orbital symmetry of the plane’s electronic states may be influencing the tunneling process and is responsible for the strange behavior we observed at the surface."



Surface-sensitive techniques, such as electron tunneling and photoemission, have been crucial in gleaning information about high-temperature superconductors, Yazdani said. But it hasn’t always been clear from which layer the information was coming. By imaging at the atomic scale and probing on the nanoscale, the researchers achieved much higher precision.

"High-temperature superconductors are layered compounds containing one or more copper-oxide planes and other layers that act as charge reservoirs," Yazdani said. "Like dopants in a semiconductor, these layers donate charge carriers to the copper-oxide planes, making them conducting. The strong electronic interactions in the copper-oxide planes are responsible for the material’s unusual electronic properties."

To image the surface of thin films of superconducting crystal, Yazdani and his colleagues used a low-temperature scanning tunneling microscope that they built at Illinois. By exploring large areas of the sample and correlating the STM topographic images with X-ray crystallographic data, the researchers were able to identify individual layers of copper oxide and of bismuth oxide, and then measure their electronic properties.

"With the STM, we can send electrons through the tip and measure the rate at which they flow into the surface," Yazdani said. "We found a very strong contrast in the spectra taken on the two surfaces. The electron tunneling in the copper-oxide plane was strongly suppressed at low energies."

This behavior is unexpected in a d-wave superconductor, Yazdani said, and could demonstrate the dramatic influence of the layered structure on the surface electronic properties. The observations can best be explained by the way in which the STM tip couples to the electronic states of the copper-oxide plane, the researchers concluded.

"At low energies, electrons from the tip are constrained by the orbital symmetry of the plane’s electronic wave function, which resembles a cloverleaf pattern," Yazdani said. "This directional dependence of the current can explain the suppressed tunneling."

Previous measurements had been performed on surfaces terminated with other layers – bismuth oxide, for example – where the copper-oxide plane was buried under the surface. In those experiments, however, it was not apparent how the STM tip was coupling to the copper-oxide plane, Yazdani said.

"You could theorize that the other layers had no effect on the measurement, but that flies in the face of our experiment," Yazdani said. "From our results, it is clear that what you put at the surface makes a huge difference in what you measure."

Having direct access to the surface means scientists can begin manipulating its properties by changing what’s under the surface. The Illinois work also opens a new methodology for probing electrons in the copper-oxide plane.

Collaborators on the project were physics professor James Eckstein, postdoctoral research associate Tiziana DiLuccio, and graduate students Seongshik Oh and Daniel Hornbaker. The National Science Foundation, Office of Naval Research and the U.S. Department of Energy funded the work.

Jim Kloeppel | UIUC News Bureau
Further information:
http://www.news.uiuc.edu/

More articles from Physics and Astronomy:

nachricht NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center

nachricht Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>