Superconductors at room temperature can convert everything from electrical networks to particle accelerators to computers – but before they can be implemented, researchers need to better understand how existing high-temperature superconductors work.
Now researchers from the National SLAC Accelerator Laboratory of the Department of Energy, the University of British Columbia, Yale University and others have taken a step in this direction by studying the rapid dynamics of a material called yttrium-barium-copper oxide, or YBCO.
The team reports May 20 Science that the superconductivity of YBCO is unexpectedly intertwined with another phenomenon known as charge density waves (CHDs), or ripples in the electron density in the material. As researchers expected, CDWs become stronger when YBCO superconductivity is turned off. However, they were surprised to find that VZP also suddenly became more spatially organized, suggesting that superconductivity somehow fundamentally shapes the shape of VZP on a nanoscale.
“Much of what we don’t know is the relationship between charge density waves and superconductivity,” said Giacomo Kaslawicz, a researcher at the National Accelerator Laboratory of the SLAC Department of Energy who led the study. “As one of the cleanest high-temperature superconductors that can be grown, YBCO offers us the opportunity to understand this physics in a very direct way, minimizing the effects of clutter.”
He added: “If we can better understand these materials, we will be able to create new superconductors that operate at higher temperatures, allowing the use of many other applications and potentially solving many social problems – from climate change to energy efficiency and fresh water availability.”
Observing fast dynamics
The researchers studied the dynamics of YBCO on an X-ray laser SLAC with a coherent light source (LCLS). They eliminated superconductivity in YBCO samples using infrared laser pulses and then repelled X-ray pulses from these samples. For each X-ray image, the team compiled a unique CDW electronic pulsation image. Gluing them together, they resumed the rapid evolution of CDW.
“We did these experiments at LCLS because we needed ultrashort X-ray pulses that could be done in very few places in the world. And we also needed soft X-rays that have longer wavelengths than regular X-rays to make. discover CDW, ”said full-time scientist and co-author of the study Joshua Turner, who is also a researcher at the Stanford Institute of Materials and Energy Sciences. “Also, it’s really nice to work with people at LCLS.”
These LCLS experiments generate terabytes of data that are difficult to process. “Using many hours of supercomputing time, LCLS beamline scientists have gathered our vast amounts of data into a more manageable form so that our algorithms can highlight characteristics,” said Maine Singh (Katie) Na, a graduate student and co-author of the University of British Columbia. on the project.
The team found that charge density waves in YBCO samples became more correlated – that is, more electronic pulsations were periodic or spatially synchronized – after the lasers turned off the superconductivity.
“Doubling the number of waves that are only related to a flash of light is very surprising because light tends to produce the opposite effect. We can use light to completely destroy the charge density waves if we press too hard, ”Kaslavich said.
To explain these experimental observations, the researchers modeled how the areas of VZP and superconductivity should interact, given the many basic assumptions about how YBCO works. For example, their original model assumed that a homogeneous region of superconductivity when turned off by light would become a homogeneous region of GDP – but, of course, this does not coincide with their results.
“The model that best fits our data shows that superconductivity acts as a defect in the wave pattern. This indicates that the waves of superconductivity and charge density like to settle down in a very specific, nanoscopic way, ”Kaslavich explained. “They are intertwined orders on the scale of the wavelengths themselves.”
Illuminating the future
Kaslavich said that the ability to turn off superconductivity using light pulses has been a significant advance, allowing observations to be made on a time scale of less than a trillionth of a second with great advantages over previous approaches.
“If you use other methods, such as applying a strong magnetic field, you have to wait a long time before taking measurements so that CDWs are rebuilt around the mess and other phenomena can take place in the sample,” he said. “The use of light has allowed us to show that this is an intrinsic effect, a real connection between superconductivity waves and charge density.”
Turner said the research team is excited to expand this important work. First, they want to explore how VZPs become more organized when superconductivity is turned off by light. They also plan to adjust the wavelength or polarization of the laser in future LCLS experiments in hopes of also using light to amplify, rather than dampen, the superconducting state so they can easily turn the superconducting state on and off.
“There is a common interest in trying to do this with light pulses on a very fast time scale because it could potentially lead to the development of superconducting light-controlled devices for a new generation of electronics and computing,” Kaslavich said. “Ultimately, this work can also help people trying to build superconductors at room temperature.”
This study is part of a collaboration between researchers from LCLS, Stanford Synchrotron Radiation (SSRL), UBC, Yale University, the National Institute of Research in Canada, North Carolina State University, Brescia Catholic University and other institutions. This work was partially funded by the US Department of Science. LCLS and SSRL are user objects of the Office of Science of the Ministry of Science.