Promise Lies Ahead for Superconductivity After 100 Years
The centennial celebration of superconductivity was the talk of this year’s March Meeting. Both researchers and historians took time to reflect on the serendipitous discovery of superconductivity, and speculate about its future promise for the world. The Kavli Foundation sponsored two sessions on the history and future of the effect, one of which featured five Nobel Laureates. Dozens of sessions focused on applications and basic research in the field. Even before the meeting started, the Industrial Physics Forum, organized by the American Institute of Physics, highlighted current and future areas of research and industrial applications.
A common theme for those speaking was how the story of superconductors has been filled with unexpected discoveries. In 1911, Heike Kamerlingh Onnes, the Dutch physicist who would later win a Nobel Prize for liquefying helium, was measuring the resistance of mercury when his instruments showed that it dropped to zero at four degrees Kelvin. At first he thought the results stemmed from a short in his equipment because it was an effect that no one had predicted.
Once he realized that his experiments were sound, this unexpected effect became the focus of intense study. From the start, the promise of dissipationless electricity was evident. Laura Greene of the University of Illinois at Urbana-Champaign pointed to a press release from Onnes’ lab in 1920 that said superconductivity would lead to “better energy storage, better magnets and helping the energy crisis.”
Today superconductivity continues to be an active field of research. Five Nobel prizes have been awarded for research on understanding the mechanisms behind superconductors. Materials physicists the world over have been working to develop high temperature superconductors.
“Materials are very important for superconductivity. In fact they drove most of the advances in the last century,” said George Crabtree of Argonne National Laboratory. “Superconductivity has in many ways led the field of condensed matter physics.”
An ultimate goal is to develop a material that superconducts at room temperature. It’s been a long and difficult search. Researchers have been pushing the envelope slowly but surely. For the first seventy years or so, the high temperature limit of superconductors kept climbing on average of about a degree a year.
Then in 1986, scientists at IBM’s Zurich Research Lab discovered that copper-oxide-based materials can superconduct at temperatures warmer than any previously known. Soon there were examples above the temperature of liquid nitrogen. The goal of a room temperature superconductor seemed tantalizingly near. Dreams of superconducting power lines, low energy server farms and magnetic levitating trains seemed palpably close. People compared the perceived coming superconducting revolution to the way semiconductors revolutionized the world through computer processing.
As it turned out, the revolution hasn’t quite come. “It was fun actually to imagine all that stuff,” said Seamus Davis of Brookhaven National Laboratory. But he added, “it’s really not like what happened in the world of semiconductors.”
It soon became apparent that the cuprate superconductors topped out around 164 K. Then in 2008, the surprise discovery by scientists in Japan that iron- based pnictides can superconduct at temperatures as high as 55 K touched off another flurry of excitement. This opened up a whole new family of high temperature superconductors to explore. Though still far below room temperature, the discovery offered physicists hope that some new unexplored material will ultimately yield a superconductor that can work its magic without the need for cryostats.
“I don’t think that there’s anyone in the room saying you couldn’t get a room temperature superconductor,” Crabtree said.
As researchers continue to probe for a general understanding of superconductivity, new uses for the phenomenon continue to be developed. Today, the most frequently encountered use of superconductivity is in MRI machines. As early as the 1970s, it was realized that the strong magnetic fields generated by a superconducting coil would make clearer images and be more reliable than those generated from the fields of conventional magnets. Today, virtually all MRIs are built with superconducting coils generating their powerful magnetic fields.
Transporting energy is another area that laboratories and companies are actively investigating. The US power grid loses about ten percent of generated electricity in the transmission from generating plant to end user. Superconducting cables should be able to eliminate almost all of that loss. At the same time, as renewable energy becomes a bigger part of the country’s supply, the need to transfer large amounts of electricity great distances becomes imperative. With the best sources of wind power in the Midwest and solar in the Southwest, electricity will have to be transmitted hundreds of miles to reach the population centers on the east and west coasts.
Starting in 2008, the Long Island Power Authority, with support from the Department of Energy, has been testing a prototype high-temperature superconducting cable with generally positive performance results at a transmission voltage of 138 kV. The need for cooling the line and high costs of the lengths of cable has been the biggest impediment for widespread integration into the grid. However South Korea has taken the lead in actually integrating superconducting lines into its grid. The South Korean utility company KEPCO announced in 2010 that it was purchasing three million meters of superconducting wire to fabricate ten kilometers of superconducting cable for use in the country’s power grid, including three kilometers feeding directly into Seoul.
“We are at the point of an historic transition in the field of the application of high temperature superconductivity into the power grid,” said Alexis Malozemoff from the company American Superconductor which also makes superconducting wires. “[Until] US utilities show similar leadership…it looks like the Koreans are going to lead the way.”