High-temperature superconductors unlike any other material

An experiment by researchers at the University of Maryland's Centre for Superconductivity Research and at the University of Toronto provides the first clear evidence that electrons in high-temperature superconductors behave differently than electrons in any other material.

The researchers show that electrons in a copper oxide (high-temperature) superconductor violate a fundamental theory of modern physics known as the Fermi-liquid theory. The Fermi-liquid theory forms the foundation for scientists' understanding of metals.

One tenant of the landmark Fermi-liquid theory is that electrons in a metal can be treated as quasiparticles whose ability to transport heat is strictly determined by their ability to transport charge. However, the study's findings show that, in at least one type of superconductor, the electron system can conduct heat in a way that is largely unrelated to the way it carries charge.

"Our experiment shows that the very low temperature, normal metal state of so-called high-temperature superconducting materials is unlike any other material known," said Richard Greene, a professor in the University of Maryland's Department of Physics. "These findings represent a significant fundamental scientific result. And although they are not of practical significance at present, they may be a step toward someday finding a room temperature superconductor."

Superconductors are materials that conduct electricity with no resistance. The holy grail of superconducting research is the discovery of a material that will act as a superconductor at room temperature. However, all materials discovered so far must be extremely cold to be superconductors.

Currently, superconducting materials fall into two types. Low-temperature superconductors must be cooled to at least 23 degrees Kelvin. High-temperature superconductors must be around 130 degrees Kelvin.

"The Nobel Prize-winning discovery of high-temperature superconductors was made some 15 years ago," Greene said. "But in spite of intense research by condensed matter theorists and experimentalists all over the world, nobody yet understands the mechanism by which high-temperature superconductivity can occur.

Our findings provide physicists a new focal point for understanding high-temperature superconductivity. The next step will be to develop an explanation for our, as-yet unexplained, experimental results. We believe such an explanation will give new insights into the mechanism of high-temperature superconductivity and into the properties of other materials in which the interactions among the electrons are very strong and dominate the properties."