PORTLAND, Ore. -- Superconductors are heating up. A group of international scientists working with the National Accelerator Laboratory in Menlo Park, Calif., have discovered lasers that can create conditions for superconductivity at temperatures as high at 140°F. If these efforts are successful, everything from the electric grid to mobile electronics will experience a tremendous speedup while simultaneously running much cooler.
Scientists, researchers, and engineers worldwide have been searching for room temperature superconductors since the Dutch physicist Heike Kamerlingh Onnes discovered the phenomenon in 1911. Over the years, many materials have been discovered that superconduct at higher temperatures, but even the best require cooling to 90 degrees Kelvin (-297°F). Now researchers at the SLAC National Accelerator Laboratory (originally named the Stanford Linear Accelerator Center) have found that using a laser can slightly shift the positions of atoms, creating a temporary alignment that produces the conditions for picosecond pulses of superconductivity. Now they are searching for a way to extend the pulses.
Laser causes oxygen atoms (red) to vibrate between layers of copper (blue) oxide that are just two molecules thick in a common high-temperature superconducting material known as YBCO in a way that
likely indicates superconductivity.
(Image: Jörg Harms/Max Planck Institute for the Structure
and Dynamics of Matter)
"We should aim for extending it to DC in order to use it for applications," Roman Mankowsky of the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany, told EE Times. "Switching an insulator to a metallic state by light pulses is already possible in other materials."
After more than a century of research, scientists still debate why superconductors have zero resistance, but the scientists collaborating on this project are experimenting with the phase alignment of atoms in the material's lattice. The collaborators included researchers from the Max Planck Institute, the Paul Scherrer Institute in Switzerland, the National Center for Scientific Research in France, the Swiss Federal Institute of Technology, College of France, the University of Geneva, Oxford University, the Center for Free-Electron Laser Science in Germany, and the University of Hamburg.
"My most optimistic hope is that we can learn how to create a stable superconductor at room temperature without the need of any laser excitation from the structural modification and dynamics of other competing phases in this out-of-equilibrium state," Mankowsky said.
The researchers used lasers to align the lattice structure of yttrium barium copper oxide, a high-temperature superconductor (high-Tc) often called YBCO. They then viewed the actual positions of the atoms resulting in the lattice alignment properties with high-energy X-rays from the SLAC Linac Coherent Light Source (LCLS). The resulting shift in positions of the copper and oxygen atoms created picosecond pulses of perfect phase alignment that indicated superconductivity.
Mankowsky said of the experiment's technique:
The large step forward in this experiment was that we found a theory that can explain the nonlinear lattice effects and shows excellent agreement with the experiment. We can use this theory to determine certain lattice changes that we can achieve for different excitations and materials to design new experiments. Generally, I am very interested in finding ways to use this technique of nonlinear lattice control for switching macroscopic states of materials -- for example, for data storage or electronic applications.
Before DC operation and real-world applications can be achieved, however, the researchers have to learn how to extend the time of the picosecond-sized superconducting states achieved with the laser to keep the material in steady-state alignment without having to supercool it. To do that, they need to extend their theory and carefully observe the different phases of the materials. They are already starting a series of measurement experiments in different high-temperature superconductors.
"Following up on this experiment, we are exploring ways of understanding the state better and keeping the state stable for longer times," Mankowsky said. "In the cuprate materials [like YBCO], there are competing orders such as charge density wave order and the still not fully understood pseudogap [bandgaps that open only under certain conditions] that might play a role. We are designing experiments to learn about the dynamics of these competing orders."
The work was supported by the European Research Council, the German Science Foundation, the Swiss National Superconducting Center, and the Swiss National Science Foundation.
— R. Colin Johnson, Advanced Technology Editor, EE Times