November 18, 2013
Superconductors are a fascinating group of materials in which electrons can flow with almost zero resistance. They have the potential to revolutionize electronics and power distribution, but no existing superconductors have an ideal combination of properties necessary to realize these applications. To design the ideal superconductor, scientists need a complete understanding of the complex, atomic-level electrical and magnetic behaviors that produce the phenomenon.
Many groups have focused their efforts on “high-temperature” (high-Tc) superconductors that operate at temperatures well above the conventional superconducting materials. Conventional superconductors must be chilled to almost absolute zero (the coldest temperature possible), making them impractical for many applications. The most widely studied high-Tc materials, known as cuprates because they contain layers of copper and oxygen atoms, avoid the ultra-low temperature requirement, but exhibit other properties that limit their practical use.
Recently, a new family of iron-based superconductors was discovered that do not seem to superconduct in the same way as conventional superconductors or quite like the cuprates. This iron-based family has been found to be quite large and diverse, so physicists are hoping that studying all of its members will yield a clear picture of how they operate, and point the way to a high-Tc material that has other necessary properties.
(a) Data taken from 3 to 30K showing the temperature dependence of infrared transmission through the LaFeAsO1-‐xFx thin film, normalized to the transmission at 33K (b) Time-‐resolved infrared transmission data through the sample from about 2K to 15K. The slow (ns) relaxation time indicates the presence of a full superconducting gap.
In this work, researchers from Brookhaven National Laboratory and the Leibniz Institute for Solid State Physics in Dresden, Germany, investigated an iron pnictide compound composed of lanthanum (La), iron (Fe), arsenic (As), oxygen (O), and an added fluorine (F) “dopant” that replaces about 10 percent of the O atoms. Abbreviated LaFeAsO1-xFx (the ‘x’ denotes the number of F and, therefore, O atoms per molecule), it was the first iron-based superconductor found to operate at temperatures higher than most conventional superconductors. Still, little is known about how it works.
This work may be a key step in changing that. Using beams of infrared light produced at Brookhaven’s National Synchrotron Light Source, the group discovered evidence that LaFeAsO1-xFx has a full “superconducting gap” – the energy required for electrons in the lowest energy state, the ground state, to “jump” into higher energy levels. This gap is one hallmark of a superconductor and an indicator of its performance under certain conditions. For example, the gap in the cuprates actually disappears for electrons traveling in certain directions.
“Understanding the details of the gap is essential for unraveling the superconducting mechanism, yet questions about gap structure in this material have persisted even after years of research,” said Brookhaven researcher Xiaoxiang Xi, who was the lead experimenter in the study. “Establishing these details experimentally, as we have done, puts constraints on the possible theories that could explain the origin of the superconductivity in these materials.”
See the full article here.
One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
ScienceSprings is powered by MAINGEAR computers