New insights into high-temperature superconductors

Feb 26, 2007

Scientists at the Carnegie Institution's Geophysical Laboratory in collaboration with a physicist at the Chinese University of Hong Kong have discovered that two different physical parameters —pressure and the substitution of different isotopes of oxygen (isotopes are different forms of an element) —have a similar effect on electronic properties of mysterious materials called high-temperature superconductors.

The results also suggest that vibrations (called phonons), within the lattice structure of these materials, are essential to their superconductivity by binding electrons in pairs. The research is published in the February 26 - March 2 on-line edition of the Proceedings of the National Academy of Sciences.

Superconductors are substances that conduct electricity — the flow of electrons — without any resistance. Electrical resistance disappears in superconductors at specific, so-called, transition temperatures, Tc's. The early conventional superconductors had to be cooled to extremely low (below 20 K or –253ºC) temperatures for electricity to flow freely. In 1986 scientists discovered a class of high-temperature superconductors made of ceramic copper oxides that have much higher transition temperatures. But understanding how they work and thus how they can be manipulated has been surprisingly hard.

As Carnegie's Xiao-Jia Chen, lead author of the study explains: "High-temperature superconductors consist of copper and oxygen atoms in a layered structure. Scientists have been trying hard to determine the properties that affect their transition temperatures since 1987. In this study, we found that by substituting oxygen-16 with its heavier sibling oxygen-18, the transition temperature changes; such a substitution is known as the isotope effect. The different masses of the isotopes cause a change in lattice vibrations and hence the binding force that enables pairs of electrons to travel through the material without resistance. Even more exciting is our discovery that manipulating the compression of the crystalline lattice of the high-Tc material has a similar effect on the superconducting transition temperature. Our study revealed that pressure and the isotope effect have equivalent roles on the transition temperature in cuprate superconductors."

Superconducting materials can achieve their maximum transition temperatures at a specific amount of "doping," which is simply the addition of charged particles (negatively charged electrons or positively charged holes). Both the transition temperature and isotope effect critically depend on the doping level. For optimally doped materials, the higher the maximum transition temperature is, the smaller the isotope effect is.

Understanding this behavior is very challenging. The Carnegie / Hong Kong collaboration found that if phonons are at work, they would account both for the magnitude of the isotope effect, as a function of the doping level, and the variation among different types of cuprate superconductors. The study also revealed what might be happening to modify the electronic structures among various optimally doped materials to cause the variation of the superconducting properties. The suite of results presents a unified picture for the oxygen isotope effect in cuprates at ambient condition and under high pressure.

"Although we've known for some time that vibrations of the atoms, or phonons, propel electrons through conventional superconductors, they have just recently been suspected to be at work in high-temperature superconductors," commented coauthor Viktor Struzhkin. "This research suggests that lattice vibrations are important to the way the high-Tc materials function as well. We are very excited by the possibilities arising from these findings."

Source: Carnegie Institution

Explore further: New filter could advance terahertz data transmission

add to favorites email to friend print save as pdf

Related Stories

Exotic states materialize with supercomputers

Feb 12, 2015

Scientists used supercomputers to find a new class of materials that possess an exotic state of matter known as the quantum spin Hall effect. The researchers published their results in the journal Science in Dec ...

Evidence mounts for quantum criticality theory

Jan 30, 2015

A new study by a team of physicists at Rice University, Zhejiang University, Los Alamos National Laboratory, Florida State University and the Max Planck Institute adds to the growing body of evidence supporting ...

Recommended for you

New filter could advance terahertz data transmission

Feb 27, 2015

University of Utah engineers have discovered a new approach for designing filters capable of separating different frequencies in the terahertz spectrum, the next generation of communications bandwidth that ...

The super-resolution revolution

Feb 27, 2015

Cambridge scientists are part of a resolution revolution. Building powerful instruments that shatter the physical limits of optical microscopy, they are beginning to watch molecular processes as they happen, ...

A new X-ray microscope for nanoscale imaging

Feb 27, 2015

Delivering the capability to image nanostructures and chemical reactions down to nanometer resolution requires a new class of x-ray microscope that can perform precision microscopy experiments using ultra-bright ...

Top-precision optical atomic clock starts ticking

Feb 26, 2015

A state-of-the-art optical atomic clock, collaboratively developed by scientists from the University of Warsaw, Jagiellonian University, and Nicolaus Copernicus University, is now "ticking away" at the National ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.