2024-03-02 23:10:00
Hydrogen, like many of us, behaves strangely under pressure. The theory predicts that when crushed by the weight of more than a million times our atmosphere, this light, abundant and normally gaseous element first becomes a metal, and even more strangely becomes a superconductor – a material that conducts electricity with zero resistance.
Scientists are eager to understand and ultimately harness hydride-rich superconducting compounds, called hydrides, for practical purposes ranging from levitating trains to particle detectors. However, studying the behavior of these and other materials under enormous and sustained pressures is not only impractical, but measuring these behaviors is also a nightmare, if not impossible.
A breakthrough in measuring and imaging superconductors
As the calculator revolutionized arithmetic and ChatGPT revolutionized five-paragraph essay writing, Harvard researchers believe they have found a fundamental tool for the vexing problem of measuring and imaging the behavior of superconducting hydrides at high pressure.
Published in Nature, they report having integrated quantum sensors into a standard pressure device, allowing direct readings of the electrical and magnetic properties of the pressurized material.
The innovation arose from a long-standing collaboration between physics professor Norman Yao and professorBoston UniversityChristopher Laumann, who moved away from their theoretical backgrounds and delved into the practical considerations of high-pressure measurement several years ago.
The standard method for studying hydrides under extreme pressure is to use an instrument called a diamond anvil cell, which squeezes a small amount of material between two brilliant-cut diamond interfaces. To detect when a sample has been crushed enough to become superconducting, physicists typically look for a dual signature: a drop in electrical resistance to zero, as well as the rejection of any nearby magnetic fields, also known asMeissner effect.
The problem lies in capturing these details. To apply the required pressure, the sample must be held in place by a gasket that evenly distributes the compression, then enclosed in a chamber. This makes it difficult to vision » of what’s happening inside, so physicists have had to use workaround methods that involve multiple samples to measure different effects separately.
The integration of quantum sensors into a measurement tool
To solve this problem, the researchers designed and tested an ingenious retrofit: they integrated a thin layer of sensors, from natural defects in the crystal structure of the diamond, directly on the surface of the diamond anvil. They used these efficient quantum sensors, called gap centers in nitrogento image regions inside the chamber while the sample is pressurized and passes through superconducting territory.
To prove their concept, they worked with cerium hydride, a material known to become superconductive at around a million atmospheres of pressure, or what physicists call the mega-bar regime.
The impact of this discovery
This tool could help the field not only by enabling the discovery of new superconducting hydrides, but also by facilitating access to these coveted features in existing materials, for continued study.
“You can imagine that because you are now doing something in a diamond anvil cell with quantum sensors, and you can immediately see that “this area is now superconducting, this area is not”, you can optimize your synthesis and find a way to create much better samples “, concluded Christopher Laumann.
Illustration caption: Artist’s depiction of nitrogen vacancy centers in a diamond anvil cell, which can detect the expulsion of magnetic fields by a high-pressure superconductor. Credit: Ella Marushchenko
Article: “Imaging the Meissner effect in hydride superconductors using quantum sensors” – DOI: 10.1038/s41586-024-07026-7
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