Researchers find superconductivity and pseudogap compete in copper-based materials

Researchers in Quebec have directly observed a competitive relationship between superconductivity and a mysterious quantum state in copper-based materials. The team from the Institut national de la recherche scientifique used pulses of light to temporarily suppress superconductivity, revealing that the pseudogap state emerges in its place. The findings, published in Nature Physics, provide new insight into the behaviour of high-temperature superconductors. The work was supported by funding from the Canada Foundation for Innovation and the Natural Sciences and Engineering Research Council of Canada.

The experiment was conducted using a time- and angle-resolved photoemission spectroscopy system at the Advanced Laser Light Source laboratory at INRS. By hitting a cuprate material with a light pulse, the researchers were able to momentarily lift its superconducting state. "Thanks to the unique capabilities of the TR-ARPES system at the ALLS laboratory at INRS, we were able to directly observe what happens when superconductivity temporarily disappears and then re-emerges," said Dario Armanno, a PhD student at INRS and first author of the study. Armanno described the observation as "a bit like uncovering missing frames from a film that scientists have been trying to piece together for decades." When superconductivity was suppressed, the pseudogap immediately appeared, and the pseudogap diminished as superconductivity returned. This dynamic challenges previous ideas that the pseudogap might be a precursor that enables superconductivity.

"The pseudogap is one of the greatest mysteries in condensed-matter physics," said Professor Fabio Boschini, who led the research. "Understanding how it interacts with superconductivity is essential if we want to explain why these materials can carry electricity without energy loss at unusually high temperatures." The observation moves beyond correlation to demonstrate that the two states actively suppress each other. The research also allowed the team to access previously hidden electronic states through the light-induced manipulation. This provides a new method for studying these elusive states, circumventing limitations of conventional techniques. Olivier Gingras, an associate research scientist at the Flatiron Institute's Center for Computational Quantum Physics, said the pseudogap and superconducting states in cuprates are among the most complex phenomena to reproduce theoretically.

"Our study reveals that they compete with one another and provides new insight into their behavior when both are excited simultaneously," Gingras said. The findings have implications for the development of future quantum technologies and contribute to Canada's National Quantum Strategy. The research builds on the foundation laid by the 1986 discovery of cuprates, materials that hold the potential for lossless electricity transmission. Professor Boschini is a specialist in ultrafast spectroscopy of quantum condensed matter at INRS. The ability to manipulate quantum states within cuprates offered the team a novel way to probe their interplay. Funding for the work at ALLS also came from the Alfred P. Sloan Foundation and the Canada Foundation for Innovation's Major Science Initiatives Fund. The precise mechanisms governing cuprate superconductivity remain a challenge nearly 40 years after their discovery.

With files from Quantum Zeitgeist