Scientists at SLAC National Accelerator Laboratory have glimpsed the signature of PDW, and confirmed that it intertwines with CDW stripes, which are created when SDW stripes emerge and intertwine. Image: Jun-Sik Lee/SLAC National Accelerator Laboratory.Unconventional superconductors contain a number of exotic phases of matter that are thought to play a role, for better or worse, in their ability to conduct electricity with 100% efficiency at much higher temperatures than scientists had previously thought possible. At the moment, though, these temperatures are still too low for the widespread deployment of unconventional superconductors in perfectly efficient power lines, maglev trains and so on.
Now, scientists at the US Department of Energy's SLAC National Accelerator Laboratory have glimpsed the signature of one of those phases, known as pair-density waves (PDW). This has allowed them to confirm that this phase is intertwined with another phase known as charge density wave (CDW) stripes – wavelike patterns of higher and lower electron density. The scientists report their findings in a paper in Physical Review Letters.
Observing and understanding PDW and its correlations with other phases may be essential for understanding how superconductivity emerges in unconventional superconductors, allowing electrons to pair up and travel with no resistance, said Jun-Sik Lee, a SLAC staff scientist who led the research at the lab's Stanford Synchrotron Radiation Lightsource (SSRL).
Even indirect evidence of the PDW phase intertwined with charge stripes is an important step on the long road toward understanding the mechanism behind unconventional superconductivity, which has eluded scientists over more than 30 years of research.
To make this latest observation, Lee and his colleagues had to dramatically increase the sensitivity of a standard X-ray technique known as resonant soft X-ray scattering (RSXS) so it could see the extremely faint signals given off by these phenomena. According to Lee, this technique has potential for directly sighting both the PDW signature and its correlations with other phases in future experiments, which is what they plan to work on next.
The existence of the PDW phase in high-temperature superconductors was proposed more than a decade ago and it's become an exciting area of research, with theorists developing models to explain how it works and experimentalists searching for it in a variety of materials.
In this study, the researchers went looking for it in a copper oxide, or cuprate, material known as LSCFO for the elements it contains – lanthanum, strontium, copper, iron and oxygen. It's thought to host two other phases that may intertwine with PDW: CDW stripes and spin density wave (SDW) stripes.
The nature and behavior of charge and spin stripes have been explored in a number of studies, but there have only been a few indirect glimpses of PDW – much like identifying an animal from its tracks – and none were made with X-ray scattering techniques. Because X-ray scattering reveals the behavior of an entire sample at once, it's thought to be the most promising way to clarify whether PDW exists and how it relates to other key phases in cuprates, Lee said.
Over the past few years, the SSRL team has worked on increasing the sensitivity of RSXS so it could capture the signals they were looking for.
Postdoctoral researcher Hai Huang and SLAC staff engineer Sang-Jun Lee used the improved technique in this study. They scattered X-rays off LSCFO and into a detector, forming patterns that revealed what was going on inside the material. As they dropped the temperature of the material toward its superconducting range, SDW stripes appeared and intertwined to form CDW stripes, which were then associated with the emergence of two-dimensional fluctuations that are the hallmark of PDW.
The researchers said these results not only demonstrate the value of the new RSXS approach, but also support the possibility that the PDW is present not just in this material, but in all the superconducting cuprates.
This story is adapted from material from SLAC National Accelerator Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.