Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

’Electronic crystal’ in high-temperature superconductor

27.08.2004


In a standard scanning tunneling microscope image, left, the atoms in a cuprate crystal the bright blobs) are not in a particularly orderly arrangement. But an image of the probable distribution of electrons, right, shows that clouds of them have arranged themselves in what amounts to an electronic crystal. The brighter areas seem to contain more electrons, but the reason for this is unknown.


To protect the instrument from outside vibrations, the modified STM at Cornell is enclosed in a sealed, isolated room mounted on massive supports. Copyright © Cornell University


With equipment so sensitive that it can locate clusters of electrons, Cornell University and University of Tokyo physicists have -- sort of -- explained puzzling behavior in a much-studied high-temperature superconductor, perhaps leading to a better understanding of how such superconductors work.

It turns out that under certain conditions the electrons in the material pretty much ignore the atoms to which they are supposed to be attached, arranging themselves into a neat pattern that looks like a crystal lattice. The behavior occurs in a phase physicists have called a "pseudogap," but because the newly discovered arrangement looks like a checkerboard in scanning tunneling microscope (STM) images, J.C. Séamus Davis, Cornell professor of physics, calls the phenomenon a "checkerboard phase."

Davis, Hidenori Takagi, professor of physics at the University of Tokyo, and co-workers describe the observations in the Aug. 26, 2004, issue of the journal Nature. An article about the work also is scheduled to appear in the September issue of Physics Today.



"In at least one cuprate high-temperature superconducting material that phase is an electronic crystal," Davis reports. "We don’t understand what we’ve found, but we have moved into unknown territory that everyone has wanted to explore. Many people have believed that to understand high-temperature superconductivity we have to look in this territory."

A superconductor is a material capable of conducting electricity with virtually no resistance. Modified crystals of copper oxide, known as cuprates, can become superconductors at temperatures up to about 150 Kelvin (-123 degrees Celsius or --253 degrees Fahrenheit) when they are doped with other atoms that create "holes" in the crystal structure where electrons would ordinarily be. These superconductors are widely used in industry, although there is still no clear explanation of how they work. Their superconducting behavior begins when about 10 percent of the electrons have been removed, but for over a decade physicists have been puzzled by what happens when somewhat fewer electrons are removed: The material conducts electricity, but just barely. In theory it shouldn’t conduct at all.

Davis has now been able to observe this phase with a specially modified STM that measures, in effect, the quantum wave functions of the electrons in a sample.

The famous Heisenberg uncertainty principle says that we can never tell exactly where an electron is. Rather than thinking of electrons orbiting the nuclei of atoms like little planets, scientists today imagine "clouds" of electrons somewhere in the vicinity. An STM uses a needle so fine that its tip consists of just one atom, scanning across a small surface and measuring current flow between the surface and the tip. Conventional STMs scan with enough precision to image individual atoms. Davis has increased the scanning precision to a point where he can resolve details smaller than atoms. His new instrument, located in the basement of the Clark Hall of Science on the Cornell campus, is so sensitive that it has been built in a room mounted on heavy concrete pillars and isolated by air springs. For these experiments, it scans a sample and reads the probability that electrons are in certain locations, based on current flow through the STM tip.

Davis’s team studied a copper oxide containing calcium and chlorine that was doped by replacing some of the calcium atoms with sodium to remove, in various samples, from 8 to 12 percent of the electrons. The material was cooled to about 100 milliKelvins, or a hundredth of a degree above absolute zero.

What they found was that the electrons in the sample arranged themselves in tiny squares, all in turn arranged in a neat checkerboard pattern. The same pattern was found at the highest level of doping tested, where the material begins to become superconducting. Whether or not it continues at higher levels remains to be seen, Davis says.

The discovery only leads to more questions. Theoretically, Davis says, this arrangement should not conduct electricity at all, because the electrons are locked into their crystal-like pattern. "It’s always been a mystery, how do you get from an insulator through a tiny change to a superconductor," he notes. "Having empirical knowledge of what this phase is may help us to get from here to there."

The Nature paper is titled "Discovery of a ’Checkerboard’ Electronic Crystal State in Lightly Hole-Doped Ca2-xNaxCuO2Cl2." Along with Davis and Takagi, co-authors include Cornell post-doctoral researchers Christian Lupien and Yuki Kohsaka; Dung-Hai Lee, University of California-Berkeley professor of physics; and Tetsuo Hanaguri of the RIKEN Institute in Japan. The cuprate material used in the experiments were prepared by Yuki Kohsaka at the University of Tokyo in collaboration with the scientists who developed it in 1995, Masaki Azuma and Mikio Takano of Kyoto University.

Bill Steele | EurekAlert!
Further information:
http://www.cornell.edu
http://www.physics.cornell.edu/profpages/Davis.htm

More articles from Physics and Astronomy:

nachricht Smallest transistor worldwide switches current with a single atom in solid electrolyte
17.08.2018 | Karlsruher Institut für Technologie (KIT)

nachricht Protecting the power grid: Advanced plasma switch for more efficient transmission
17.08.2018 | DOE/Princeton Plasma Physics Laboratory

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: Color effects from transparent 3D-printed nanostructures

New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference

Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...

Im Focus: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

LaserForum 2018 deals with 3D production of components

17.08.2018 | Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

 
Latest News

Smallest transistor worldwide switches current with a single atom in solid electrolyte

17.08.2018 | Physics and Astronomy

Robots as Tools and Partners in Rehabilitation

17.08.2018 | Information Technology

Climate Impact Research in Hannover: Small Plants against Large Waves

17.08.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>