A new superconducting compound offers a bridge to more practical superconductors with a potentially attractive range of applications, according to new research. And the new material’s strange magnetic behavior recalls classic superconductors of decades ago—but this time in a material that’s already demonstrated its near-room-temperature bona fides.
Lanthanum hydrides—which combine atoms of the rare earth metal lanthanum with atoms of hydrogen—contain a range of superconducting materials of varying properties. One noteworthy material is lanthanum decahydride (LaH10), which boasts the world’s highest accepted superconducting transition temperature, at –23 °C. (The catch is that to achieve this feat, lanthanum decahydride must be subjected to 200 billion pascals of pressure.)
Now a different lanthanum hydride (La4H23) has revealed similar if not quite equally impressive superconductivity stats. (Its transition temperature is –168 °C at 122 billion Pa.) However, the new lanthanum hydride also has revealingly peculiar magnetic properties that suggest an unexpected family resemblance to the superstar of the superconductivity world, cuprates.
If lanthanum hydrides are newcomers to superconductivity, cuprates are their old, establishment counterparts. Since the 1980s, scientists have studied cuprates like yttrium barium copper oxide (YBCO) and bismuth strontium calcium copper oxide (BSCCO) with critical temperatures above the –196 °C boiling point of liquid nitrogen—and which, crucially, don’t need unearthly pressures. Even if LaH10 does have a higher critical pressure, cuprates are more practical for real-world use, especially in magnetism-heavy applications like MRI machines, particle accelerators, and maglev trains.
The researchers call La4H23 a “bridge” between the promising lanthanum hydrides and the more practical cuprates. They now want to better understand that bridge, which could lead to important insights connecting the workhorse cuprate superconductors with the promising lanthanide upstarts—whose higher transition temperatures suggest new frontiers ahead with encroaching proximity to room-temperature superconductivity.
Magnets turn strangeness factor up
“What is impressive about this study is that the authors have been able to measure the resistivity under extremely high magnetic fields,” said James Walsh, a chemist at the University of Massachusetts Amherst, who was not involved in the new research.
When the lanthanum hydride researchers put La4H23 under magnetic fields stronger than its critical magnetic field—breaking its superconducting spell—they saw some unexpected material behaviors. Magnetic fields tend to increase electrical resistance in most metals, but in this high-magnetism state, their material’s resistance sharply dropped instead. Additionally, most metals become less resistant as they cool. But chilled below around –233 °C, the material’s resistance actually rose as its temperature kept decreasing.
“Although high critical temperatures have been a major goal in the field of superconductivity, the critical magnetic field is also important,” said Walsh. “This is especially true for applications that use the superconducting state to generate high magnetic fields.”
Lanthanum hydrides have glittered at the front of the superconductor stage since 2020. That year, scientists showed that lanthanum dihydride became a superconductor at –23 °C at the previously noted fraction-of-a-terapascal level of pressure.
Putting aside repeated claims that other scientists have failed to replicate, –23 °C is the closest researchers have come to room-temperature superconductivity. Naturally, lanthanum decahydride‘s discovery sent scientists scrambling after other lanthanum hydrides. La4H23 was one of them. In 2022, one team crafted La4H23 alongside six other lanthanum hydrides.
The authors, led by Jianning Guo of Jilin University, in China, published their work in April in the journal National Science Review.
