Room-Pressure Superconductor Breaks Temperature Record
A team of US researchers has set a new record for high-temperature superconductivity at ambient pressure [1]. With a recently developed method of sample pressurization, the group led by Liangzi Deng and Ching-Wu Chu at the University of Houston successfully locked a high-temperature superconductor called Hg1223 in a metastable phase—allowing it to superconduct under room-pressure conditions at temperatures 18 degrees higher than previously measured. The same pressurization technique could potentially be used to stabilize desired states in magnetic and thermoelectric materials under ambient conditions.
Since superconductivity was discovered in 1911, researchers have strived to trigger the effect at ever-higher temperatures. For decades, the highest recorded critical temperatures (the transition point between normal and superconducting phases) never reached far beyond 20 K, which meant the materials had to be cooled with liquid helium or hydrogen. A breakthrough came in 1986 with the discovery of cuprate superconductors—composed of alternating layers of copper oxides and other metal oxides. The unprecedently high critical temperatures of these materials ignited a frenzy of activity within the physics community.
One of the “stars” of this cuprate revolution was YBCO, a perovskite-like cuprate with the formula YBa2Cu3O7– . Discovered in 1987 by a team led by Chu, YBCO was the first material to superconduct above 77 K, the boiling point of liquid nitrogen. This warmer temperature meant that the superconducting state was far more attainable than before. The achievement heralded a flood of new discoveries, one of which was Hg1223. This mercury-based cuprate (HgBa2Ca2Cu3O8+ ) was shown in 1993 to superconduct at temperatures as high as 133 K. “This established a record high critical temperature at ambient pressure,” Chu says.
Higher-temperature superconductors have been found since then, but these materials have only reached their critical temperatures under extremely high pressures. In this regard, the 1993 ambient-pressure record had remained unsurpassed up until now.
In their latest study, Deng and Chu’s team introduce a new approach to breaking this 33-year stalemate. The team used high-pressure conditions to lock Hg1223 in a metastable phase with a higher critical temperature than its original, lower critical temperature phase. This technique, named the pressure-quench protocol (PQP), was demonstrated previously by the team using other lower-temperature superconductors. The protocol involves a diamond-anvil cell: A device most often used in fields like geology and engineering to generate extreme pressures between the tips of two opposing diamonds.
PQP comprises three key stages. First, the researchers measured the critical temperature of Hg1223 at various pressures up to 30 GPa (which is 300,000 times atmospheric pressure). They then used these observations to identify a desired metastable phase characterized by an initial, or “quenching,” pressure.
The next step was to place a sample in the anvil cell under the quenching pressure and then rapidly release the pressure at a controlled quenching temperature of 4.2 K. This rapid decompression ensured that the material remained trapped in its metastable phase. Finally, “the pressure-quenched sample was retrieved from the diamond-anvil cell with minimum disturbance and characterized outside the cell at ambient pressure via different probes,” Deng says.
Throughout the process, the researchers monitored the resistivity of their sample using specialized electrical contacts. After the newly formed phase was depressurized in the third step and recovered at ambient pressure, the team varied the temperature and identified the critical temperature as the point where the electrical resistance dropped abruptly. This evidence of a superconducting transition was further backed up by observing the expulsion of externally applied magnetic fields within the sample.
Deng, Chu and their colleagues tested several samples at different quenching pressures. In all the samples, the measured critical temperature was above normal, with the highest case reaching 151 K—some 18 degrees higher than the 1993 record.
Using synchrotron x-ray diffraction, the team found that the Hg1223 samples retained their tetragonal crystal structure following the pressurization process. However, the x-ray data also showed—through a broadening of the diffraction lines—that defects had emerged during the pressure quenching. “These defects, together with oxygen-related disorder, may be critical to stabilize the metastable phase,” Chu explains. Further evidence for this influence came from thermal annealing, in which gentle heating allowed defects in the samples to relax. During this annealing, the materials showed a change in their critical temperature, indicating a reversal from the metastable phase back to the original phase.
With the early success of their approach, the researchers are now confident that PQP will establish a new paradigm for stabilizing superconductors at ambient pressure. Although the resulting metastable state must be carefully preserved to avoid unwanted heating, the technique offers a new route to inducing high-temperature superconductivity under accessible laboratory conditions.
Beyond superconductors, PQP could be used to lock advanced materials—such as skyrmion-hosting magnetic materials and high-performing thermoelectrics—in metastable phases that are normally only accessible at high pressures. “This capability opens pathways to investigate previously inaccessible physical phenomena and bridges the gap between fundamental discoveries and practical technologies,” Deng says.
“This result will be widely noted in the superconductivity community, and I expect that many experimentalist groups will apply the same methodology to other candidate materials,” comments Ivan Božović, an expert in high-temperature superconductivity at Brookhaven National Laboratory in New York who wasn’t involved in this research. He adds that theorists will want to model the pressure process in order to guide the search for new, metastable high-temperature superconductors. “The phase space is enormous, and it is hard even to imagine its limits,” Božović says.
–Sam Jarman
Samuel Jarman is a science writer based in the UK.
References
- L. Deng et al., “Ambient-pressure 151-K superconductivity in HgBa2Ca2Cu3O8+ via pressure quench,” Proc. Natl. Acad. Sci. U.S.A. 123, e2536178123 (2026).