Superconductivity and charge density waves caught intertwining at the nanoscale

The team aimed infrared laser pulses at the YBCO sample to switch off its superconducting state, then used X-ray laser pulses to illuminate the sample and examined the X-ray light scattered from it. Their results revealed that regions of superconductivity and charge density waves were arranged in unexpected ways. (Courtesy Giacomo Coslovich/SLAC National Accelerator Laboratory)

Room-temperature superconductors could transform everything from electrical grids to particle accelerators to computers – but before they can be realized, 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 fast dynamics of a material called yttrium barium copper oxide, or YBCO.

The team reports May 20 in Science that YBCO’s superconductivity is intertwined in unexpected ways with another phenomenon known as charge density waves (CDWs), or ripples in the density of electrons in the material. As the researchers expected, CDWs get stronger when they turned off YBCO’s superconductivity. However, they were surprised to find the CDWs also suddenly became more spatially organized, suggesting superconductivity somehow fundamentally shapes the form of the CDWs at the nanoscale.

“A big part of what we don’t know is the relationship between charge density waves and superconductivity,” said Giacomo Coslovich, a staff scientist at the Department of Energy’s SLAC National Accelerator Laboratory, 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 disorder.”

He added, “If we can better understand these materials, we can make new superconductors that work at higher temperatures, enabling many more applications and potentially addressing a lot of societal challenges – from climate change to energy efficiency to availability of fresh water.”

Observing fast dynamics

The researchers studied YBCO’s dynamics at SLAC’s Linac Coherent Light Source (LCLS) X-ray laser. They switched off superconductivity in the YBCO samples with infrared laser pulses, and then bounced X-ray pulses off those samples. For each shot of X-rays, the team pieced together a kind of snapshot of the CDWs’ electron ripples. By pasting those together, they recreated the CDWs rapid evolution.

“We did these experiments at the LCLS because we needed ultrashort pulses of X-rays, which can be made 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 the CDWs,” said staff scientist and study co-author Joshua Turner, who is also a researcher at the Stanford Institute for Materials and Energy Sciences. “Plus, the people at LCLS are really great to work with.”

These LCLS runs generated terabytes of data, a challenge for processing. “Using many hours of supercomputing time, LCLS beamline scientists binned our huge amounts of data into a more manageable form so our algorithms could extract the feature characteristics,” said MengXing (Ketty) Na, a University of British Columbia graduate student and co-author on the project.

The team found that charge density waves within the YBCO samples became more correlated – that is, more electron ripples were periodic or spatially synchronized – after lasers switched off the superconductivity.

“Doubling the number of waves that are correlated with just a flash of light is quite remarkable, because light typically would produce the opposite effect. We can use light to completely disorder the charge density waves if we push too hard,” Coslovich said.

Blue areas are superconducting regions, and yellow areas represent charge density waves. After a laser pulse (red), the superconducting regions are rapidly turned off and the charge density waves react by rearranging their pattern, becoming more orderly and coherent. (Greg Stewart/SLAC National Accelerator Laboratory)

To explain these experimental observations, the researchers then modeled how regions of CDWs and superconductivity ought to interact given a variety of underlying assumptions about how YBCO works. For example, their initial model assumed that a uniform region of superconductivity when shut off with light would become a uniform CDW region – but of course that didn’t agree with their results.  

“The model that best fits our data so far indicates that superconductivity is acting like a defect within a pattern of the waves. This suggests that superconductivity and charge density waves like to be arranged in a very specific, nanoscopic way,” explained Coslovich. “They are intertwined orders at the length scale of the waves themselves.”

Illuminating the future

Coslovich said that being able to turn superconductivity off with light pulses was a significant advance, enabling observations on the 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 rearrange around disorder and other phenomena can take place in the sample,” he said. “Using light allowed us to show this is an intrinsic effect, a real connection between superconductivity and charge density waves.”

The research team is excited to expand on this pivotal work, Turner said. First, they want to study how the CDWs become more organized when the superconductivity is shut off with light. They are also planning to tune the laser’s wavelength or polarization in future LCLS experiments in hopes of also using light to enhance, instead of quench, the superconducting state, so they could readily turn the superconducting state off and on.

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

This research is part of a collaboration between researchers from LCLS, SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), UBC, Yale University, the Institut National de la Recherche Scientifique in Canada, North Carolina State University, Universita CAattolica di Brescia and other institutions. This work was funded in part by the DOE Office of Science. LCLS and SSRL are DOE Office of Science user facilities.

Citation: Scott Wandel et al., Science, 20 May 2022 (10.1126/science.abd7213)

This is a reposting of my news feature courtesy of Stanford Linear Accelerator Laboratory.

Researchers at SLAC Study Promising Alternative to Morphine

Morphine is a common narcotic pain reliever with significant side effects (sfxeric/Flickr).
Morphine is a common narcotic pain reliever with significant side effects (sfxeric/Flickr).

Morphine is a powerful narcotic, commonly used to treat moderate to severe pain from surgery, injury and chronic health conditions like cancer or osteoarthritis. However, morphine has many negative side effects. It can cause drowsiness, nausea, vomiting, dizziness and constipation. More troubling, people can become dependent on it.

According to the Centers for Disease Control and Prevention, narcotic dependence and overdose deaths are a growing health problem in the United States. Narcotic sales quadrupled from 1999 to 2010 and narcotic-related deaths more than tripled from 1999 to 2012. More than 2 million people in the U.S. currently abuse narcotics.

In order to address this problem, researchers have long searched for alternative drugs that effectively relieve pain without inducing dependence as morphine does. A team of researchers now believe they’ve found a good candidate for such a drug, although it will be a long time before this drug, if it proves to be effective, is available in stores.

These researchers are studying their new kind of pain reliever using an ultrabright, ultrafast X-ray source called the Linac Coherent Light Source (LCLS), which is located at SLAC National Accelerator Laboratory.

The LCLS creates the brightest X-ray source on the planet, which researchers need to accurately study the structure of tiny, nanoscale drug compounds.

How Narcotics Work

Narcotics are also called opioid pain relievers, because they block the sensation of pain by binding to opioid receptors within the pain pathway of the brain. A drug can provide pain relief by binding to one of three types of opioid receptors in the brain: delta, mu and kappa. Narcotics like morphine target the opioid mu receptors.

The problem is that long-term use of morphine reduces the number of available opioid mu receptors. As a result, tolerance develops so a higher dose of the drug is needed to achieve the same level of pain relief. Ultimately, prolonged use leads to physical dependence — which is when the neurons adapt to the presence of the drug and function normally only when it’s in the body.

Previous research has shown that administering morphine with another drug that simultaneously blocks the opioid delta receptors prevents this morphine-induced tolerance and dependence. Researchers just need to find the right drug combination with minimal side effects.

Recently, a team of researchers, led by University of Southern California chemistry professor Vadim Cherezov, developed a drug that activates opioid mu receptors while blocking opioid delta receptors. Their drug is derived from a specialized peptide – a naturally occurring chain of amino acids. Their research results were reported in the February issue of Nature Structural and Molecular Biology.

Studying Tiny Crystals

Unfortunately, it is very difficult to study new opioid compounds like the one Cherezov recently developed.

In order to understand the structure of new compounds, scientists usually grow crystals of the compound and then hit them with X-rays. By measuring the angles and intensity of how the X-rays bounce off the crystals, they can produce a three-dimensional picture of the crystal structure.

However, it can be difficult to grow crystals large enough to use this standard method, called X-ray crystallography. Plus, you typically need to freeze the crystal to make it more rigid, rather than study it in natural conditions and temperatures. On top of that, a conventional X-ray beam might blast and destroy the small crystal before you can collect enough data.

Instead, Cherezov’s team used the Linac Coherent Light Source to perform their experiment on tiny crystals at room temperature. LCLS X-ray pulses last just a quadrillionth of a second, or 100 times faster than it takes light to travel the width of a human hair. Yet they are a billion times brighter than a conventional X-ray source.

Using this unique X-ray source with higher-intensity, very short pulses, Cherezov was able to use smaller crystals and still collect terabytes of structural data before the crystals vaporized.

Each crystal the research team prepared was a millionth of a meter and contained many copies of their new opioid compound bound to an opioid receptor. The team placed the crystals in a toothpaste-like gel to simulate the receptors’ natural environment, and then injected a thin stream of this gel into the path of the LCLS X-ray beam.

The resulting structural model was precise enough to show how the new drug molecules bind with the receptor. This atomic-scale map should help scientists develop pain-relieving drugs with fewer negative side effects. It’s likely to to take years, though, before it can be tested in humans.

“This work will provide a solid basis for the design of a new generation of pain relievers with reduced dependency,” Cherezov said in a press release.

Cherezov’s experiment is just one of many performed at the Linac Coherent Light Source.

The LCLS is a Department of Energy User Facility where approximately 600 scientists conduct groundbreaking experiments each year, across many fields, including chemistry, biology, material science, technology and energy science.

This is a repost of my KQED Science blog.

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