Distributed February 15, 2002
News Service Contact: Kate Bramson
AAAS Annual Meeting, Sunday, Feb. 17, 3 p.m.
Superconductor discovery could lead to more efficient electricity
New research has shown that type-II superconductors really superconduct – they transmit electricity without dissipating energy. Xinsheng Sean Ling, assistant professor of physics at Brown University, will discuss his team’s research, which answered a longstanding question in physics. Engineers can use this latest discovery to seek ways to distribute electricity more efficiently.
PROVIDENCE, R.I. — Type-II superconductors actually work, according to research led by Brown University physicist Xinsheng Sean Ling that solved a decades-old puzzle in physics. Now, engineers can work to develop type-II superconductors for practical purposes, such as a more efficient transmission of electricity, Ling said.
“Our work will not directly give you a better wire, but our work provides a foundation for the science behind the wires that deliver the electricity to your house in the future,” he said.
Although physicists have known since 1957 that type-I superconductors work, no one had proven whether type-II superconductors actually superconducted or merely functioned as better conductors than regular metals such as copper. Scientists generally believed that when the vortex matter inside type-II superconductors interacted with atomic impurities the vortices couldn’t form a solid phase (such as water freezing into ice). It was also believed that without such a phase transition, the defining property of a superconductor – the ability to carry electrical current without dissipation – was lost.
“Our work proves this belief was wrong,” Ling said. “Vortices can freeze into a solid phase. Now we know type-II superconductors are really working.”
A superconductor is a metal that – when cooled to below a critical temperature – allows an electrical current to run through it without dissipating energy. Wires that are effective superconductors could prevent hundreds of millions of watts of energy from being wasted as they escape through electrical wires before ever reaching homes and businesses.
There are two types of superconducting materials. Type-I superconductors such as aluminum and lead superconduct at low temperatures when electrons form “Cooper pairs.” The work of Ling and his colleagues built on a landmark theory of superconductivity developed in the 1950s by the late John Bardeen, Brown physicist Leon Cooper and Robert Schrieffer, who won the Nobel Prize in 1972 for explaining why type-I superconductors are really superconducting.
Most applications such as Magnetic Resonance Imaging (MRI) magnets require type-II superconductors such as niobium, niobium-titanium alloys and the newly discovered high-temperature superconductors, which all work in the presence of a magnetic field. For these applications, forming Cooper pairs is not enough. In type-II superconductors, the magnetic vortices induced by the magnetic field must be “pinned” or stopped so as not to destroy the defining property of superconductivity. When the vortices are pinned, the important phase transition takes place.
Prior to Ling’s research, there was only indirect evidence suggesting that vortices may undergo a phase transition of some kind. Ling’s team developed a technique that allowed them to zoom into a very narrow temperature range of a classic type-II superconductor of niobium. They then used a neutron beam to take pictures of the phase transition of the vortices.
Ling’s current research in superconductivity is funded by a three-year, $270,000 National Science Foundation grant. The researchers are in the first year of that grant. They plan to extend their research to other superconductor materials beyond niobium.
Applications of superconductors are widespread. They are used in MRI machines and in magnets for high-energy physics experiments. The 1987 discovery of high-temperature superconductors provided hope that superconductors could one day be the main carriers of electricity.
“The original motivation of superconductor research was to find a superconductor which can carry electrical current without dissipation,” Ling said. “It turns out that that moderate objective has led to a deeper understanding of the basic principles of how matter condenses in nature.”
But there is still a major hurdle preventing engineers from creating more efficient electricity, and that is metallurgy, he said. It takes time to create metals or alloys that can act as the appropriate superconductor for a specific purpose such as electricity. For example, the commercialization of the alloy used as a superconductor in MRI machines took about 20 years, Ling said.
The research team includes Ling; Brown Ph.D. student Sang Ryul Park; Bridget McClain, a Brown junior; Sungmin Choi, who was at the National Institute of Standards and Technology (NIST) and the University of Maryland and now teaches in South Korea; and Daniel Dender and Jeff Lynn of the NIST Center for Neutron Research.