Interest charge

Superconductivity and charge density waves captured at the nanoscale

Newswise – Room-temperature superconductors could transform everything from power grids to particle accelerators to computers – but before they can achieve them, researchers need to better understand how existing high-temperature superconductors work.

Now, researchers from the Department of Energy’s SLAC National Accelerator Laboratory, the University of British Columbia, Yale University and others have taken a step in that direction by studying the rapid dynamics of a material called yttrium barium copper oxide, or YBCO.

The team reports on May 20 to Science that YBCO’s superconductivity is unexpectedly intertwined with another phenomenon known as charge density waves (CDW), or ripples in electron density in the material. As the researchers expected, CDWs become more powerful when they turn off the superconductivity of YBCO. However, they were surprised to find that CDWs also suddenly became more spatially organized, suggesting that superconductivity somehow fundamentally shapes the shape of CDWs at the nanoscale.

“A lot of what we don’t know is the relationship between charge density waves and superconductivity,” said Giacomo Coslovich, a scientist at the Department of Energy’s SLAC National Accelerator Laboratory, who led the study. study. “As one of the cleanest high-temperature superconductors that can be grown, YBCO offers us the possibility of understanding this physics in a very direct way, minimizing the effects of disorder.”

He added: “If we can better understand these materials, we can make new superconductors that operate at higher temperatures, enabling many other applications and potentially addressing many societal challenges – from climate change to energy efficiency in through the availability of fresh water”.

Observe the fast dynamics

The researchers studied the dynamics of YBCO at the Linac Coherent Light Source (LCLS) X-ray laser at SLAC. They turned off the superconductivity in the YBCO samples with infrared laser pulses, then bounced the X-ray pulses off those samples. For each X-ray shot, the team reconstructed a sort of snapshot of the CDWs’ electronic ripples. By gluing them together, they recreated the rapid evolution of CDWs.

“We did these experiments at LCLS because we needed ultrashort pulses of X-rays, which can be done at very few places in the world. And we also needed soft x-rays, which have longer wavelengths than typical x-rays, to directly detect CDWs,” said study scientist and co-author Joshua Turner, who is also researcher at the Stanford Institute for Materials and Energy. Science. “Plus, the people at LCLS are really great to work with.”

These LCLS experiments generated terabytes of data, a challenge for processing. “Using many hours of supercomputing, the LCLS beamline scientists aggregated our massive amounts of data into a more manageable form so that our algorithms could extract features from features,” said MengXing (Ketty) Na, 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 electron ripples were periodic or spatially synchronized – after the lasers turned off superconductivity.

“Doubling the number of waves correlated to a single flash of light is quite remarkable, as light would generally produce the opposite effect. We can use light to completely disrupt charge density waves if we push too hard,” Coslovich said.

To explain these experimental observations, the researchers then modeled how the regions of CDWs and superconductivity should interact given a variety of underlying assumptions about how YBCO works. For example, their initial model assumed that a uniform region of superconductivity when cut by light would become a uniform region of CDW – but of course this did not agree with their results.

“The model that best fits our data so far indicates that superconductivity acts as a defect in a wave pattern. This suggests that superconductivity and charge density waves like to be arranged in very specific nanoscopic ways” , Coslovich explained, “These are interwoven orders on the scale of the length of the waves themselves.”

Light up the future

Coslovich said the ability to turn off superconductivity with light pulses was a significant advance, enabling observations on a time scale of less than a trillionth of a second, with major advantages over previous approaches.

“When you use other methods, like applying a high magnetic field, you have to wait a long time before making measurements, so CDWs reorganize around disorder and other phenomena can take place in sample,” he said. “Using light allowed us to show that this is an intrinsic effect, a real link between superconductivity and charge density waves.”

The research team is excited to expand on this crucial work, Turner said. First, they want to study how CDWs become more organized when superconductivity is cut off by light. They also plan to adjust the wavelength or polarization of the laser in future LCLS experiments in hopes of also using the light to enhance, instead of quench, the superconducting state, so they can easily activate and deactivate the superconducting state.

“There is general interest in trying to do this with pulses of light on very fast timescales, as this can potentially lead to the development of light-controlled superconducting devices for the next generation of electronics and computing. “, said Coslovich. “Ultimately, this work may also help guide people trying to build room-temperature superconductors.”

This research is part of a collaboration between researchers at LCLS, the Stanford Synchrotron Radiation Lightsource (SSRL) at SLAC, UBC, Yale University, the National Institute for Scientific Research in Canada, from North Carolina State University, Universita Cattolica di Brescia and other institutions. This work was funded in part by the DOE Office of Science. LCLS and SSRL are user facilities of the DOE Office of Science.