Superconducting temperature record set at ordinary pressures

For more than 30 years, a record in science held firm: minus 220 degrees Fahrenheit. It defined the highest achieved temperature for any material to become superconducting — able to carry electricity with no resistance — without the need for crushing pressures. In a field known for slow, steady progress, the record had come to seem almost immovable.

That limit has always been daunting because most known superconductors work only at temperatures close to absolute zero — hundreds of degrees below zero Fahrenheit. Keeping materials so ultracold requires complex and costly cooling systems. This limits where and how these materials can be applied to niche technologies, like MRI scanners and particle accelerators.

Now the record has shifted. Researchers from the University of Houston and the U.S. Department of Energy’s (DOE) Argonne National Laboratory have raised that temperature by 30 degrees, to minus 190 degrees Fahrenheit. They did so with a carefully designed oxide made of mercury, barium, calcium and copper, known as a cuprate superconductor.

“This is a major step toward practical superconductors that operate at room temperature and pressure.” — Hua Zhou, Argonne physicist and co-author in the study

Higher-temperature superconductors could allow far more efficient generation, delivery and use of electricity. They could also eventually lead to new technologies, such as more practical fusion energy systems and quantum devices.

In earlier work using Argonne’s Advanced Photon Source (APS), a DOE Office of Science user facility, scientists reported on a different material that becomes superconducting at temperatures close to room temperature. The drawback was that it worked only under pressures so intense that the material remains impractical outside specialized laboratories.

In the present project, the University of Houston team developed a method known as a pressure-quench protocol to address that challenge. They compressed a cuprate sample inside a diamond anvil cell to pressures approaching 30 gigapascals, about 300 times the pressure at the ocean bottom. Once there, the researchers rapidly released the pressure while preserving the material’s superconducting properties.

“This is a major step toward practical superconductors that operate at room temperature and pressure,” said Hua Zhou, an Argonne physicist and co-author in the study. ​“And with this material still superconducting at normal pressure, scientists can study it with widely available instruments and begin developing technologies that work under everyday conditions.”

But breaking the record is only part of the story. Understanding why it broke also matters. That is where the APS played a critical role.

The APS beamline 16-ID-B is one of the few in the world able to study materials under such extreme conditions. Its intense, tightly focused X-ray beams allowed scientists to detect subtle changes in the cuprate’s internal structure at microscopic scales during the pressure-quench process. These measurements revealed details that would otherwise remain hidden.

As explained by Maddury Somayazulu, an APS group leader at Argonne, applying such high pressure changes the distances between atoms in a material, effectively forcing them into a new arrangement. That process stores energy in the system. If the pressure is released slowly, the atoms have time to relax and return to their normal structure. But when the pressure is removed very quickly, the material can become trapped in a temporary state known as metastable. In that condition, the structure does not fully relax and instead forms many small defects.

These flaws in the orderly arrangement of atoms appear to stabilize the superconducting state. As a result, the cuprate sample can superconduct at higher temperatures without the need for continued pressure.

“That was a key insight in understanding how the pressure-quench process stabilizes the superconducting state,” Zhou said.

The findings also highlight the growing importance of advanced light sources such as the APS in modern materials science. Following a major upgrade completed in recent years, the facility now produces X-ray beams up to 500 times brighter and more tightly focused than ever before. These beams can be concentrated to sizes thousands of times smaller than a human hair, allowing researchers to map variations within materials with remarkable precision.

“With the upgraded APS, we can much better connect what happens inside a material at the microscopic level to how it performs in real-world conditions,” Somayazulu said. ​“And that’s a big deal.”

Funding sources for this research included the Enterprise Science Fund, the State of Texas, U.S. Air Force Office of Scientific Research Grants, T.L.L. Temple Foundation, John J. and Rebecca Moores Endowment and DOE Office of Basic Energy Sciences.

The research first appeared in the Proceedings of the National Academy of Science.