Researchers at the SLAC National Accelerator Laboratory have made a significant advancement in understanding unconventional superconductors. These materials can conduct electricity without loss at higher temperatures than traditional superconductors, but they still operate at extremely low temperatures, about 140 degrees Celsius below freezing. Improving their performance at warmer temperatures could lead to breakthroughs in energy and microelectronics.
The team focused on a slow process called atomic relaxation, observing its changes in the presence of two quantum states within cuprate superconductors: charge density waves (CDWs) and the superconducting state. The study was conducted using X-ray photon correlation spectroscopy at the Coherent Hard X-ray Scattering beamline (CHX) at Brookhaven National Laboratory's NSLS-II facility.
"This observation of slow atomic motion is a new way to look at things," said Joshua Turner, a principal investigator with the Stanford Institute for Materials Science and Engineering (SIMES) at SLAC. "It can tell us all sorts of interesting things about what the electrons are doing in systems and materials that many people have been studying for a long time."
Atomic relaxation can be influenced by doping, which involves introducing a new element into a material's lattice to alter its electronic properties. This process is crucial for generating superconductivity in cuprates. The dopant atoms replace some original atoms but struggle to fit comfortably due to size differences, causing them to slowly move between neighboring atoms.
Using CHX's capabilities, the team discovered that atomic relaxation took approximately 1,000 seconds in the studied cuprate. Surprisingly, atoms moved further from their average positions and relaxation slowed down when CDWs were present. As the material approached its superconducting state, this effect reversed, accelerating relaxation.
"This insight gives scientists a whole new way to explore how these quantum states intertwine on slow time scales and to understand the fundamental forces that drive unconventional superconductivity," said Lingjia Shen from SLAC's Linac Coherent Light Source (LCLS).
The research involved collaboration with scientists from MIT, Carnegie Mellon University, University of Waterloo, and Lund University. It was primarily funded by the DOE Office of Science.