An international team of researchers, including scientists from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), has achieved a methodological breakthrough in the study of superhydrides—a promising class of superconductors. For the first time, the team was able to analyze lanthanum superhydrides under extreme pressure using nuclear magnetic resonance spectroscopy.
Room-temperature superconductors
Superconductors are characterized by the fact that their electrical resistance disappears at temperatures below a critical threshold, which depends on the specific material, allowing them to conduct electricity without loss. For most known materials, this transition temperature is less than 140 kelvins (minus 133 degrees Celsius), which requires the use of sophisticated cooling technologies for practical applications. Consequently, scientists are actively searching for materials that exhibit superconductivity at higher temperatures.
Superhydrides are compounds with a high hydrogen content in which a metal, such as lanthanum, is embedded in a densely packed hydrogen lattice. Under extreme pressure, such as that found inside planets, they acquire extraordinary electronic properties and can exhibit superconductivity at nearly room temperature. As a result, this class of materials currently holds the world record for the highest critical transition temperature at which signs of superconductivity have been observed.
To create these conditions, the team compresses the samples in diamond anvils between two diamonds to pressures exceeding one million atmospheres. The challenge lies in the tiny size of the samples, which means that the research requires the highest level of experimental precision.
Microscale magnetic superlenses
The results of current research are put to use precisely here: using so-called Lenz lenses—leading microstructural ring elements—scientists precisely focus the high-frequency fields required for nuclear magnetic resonance (NMR) spectroscopy within the sample volume, thereby significantly amplifying them. This focusing makes it possible to measure NMR under extreme conditions inside a diamond cell.
The scientists had to focus the high-frequency fields precisely at the point where the sample was positioned between the diamond anvils, an area measuring just a few dozen micrometers—smaller than the diameter of a human hair. Using Lenz lenses, they were able to amplify the high-frequency signal to such an extent that meaningful NMR data for superhydrides became available for the first time.
These measurements provide direct insight into the atomic properties of materials and help us better understand them.
Combining two approaches to the study of superconductivity
Previously, the team had studied these materials using high-field pulsed magnets at the HLD facility, measuring their electrical resistance. Such magnetic fields serve as a stress test for superconductors: they make it possible to determine the maximum field strengths at which the superconducting state remains stable.
Only by combining both approaches—high-pressure NMR studies and resistance measurements in extremely strong magnetic fields—can we gain a complete understanding of the physical properties of this class of materials.
The study was conducted in close collaboration with high-pressure specialists from the High-Pressure Science and Technology Advanced Research Center (HPSTAR) in Beijing.
“The collaboration with the HLD was crucial to our project,” says Dr. Dmitrii Semenok. “The high-field facilities available there and the expertise in high-frequency instrumentation provide ideal conditions for these experiments.”
In the long term, researchers aim to gain a deeper understanding of the physical mechanisms underlying superconductivity in hydrogen-rich materials, thereby contributing to the future development of new materials for energy-efficient technologies.
According to phys.org
