Researchers have now published findings in the May 10 issue of Science that deepen our understanding of superconductivity in materials known as cuprates, which have confounded scientists since their discovery in 1986. The study focuses on the origins of their high-temperature superconductivity, which remains relatively cold.

Shiwei Zhang, a senior research scientist at the Flatiron Institute's Center for Computational Quantum Physics, noted, "There was tremendous excitement when cuprate superconductors were discovered, but no understanding of why they remain superconductive at such high temperatures." He added, "It's surprising that almost 40 years later, we still don't quite understand why they do what they do."

The breakthrough reported involves the use of a simple model, the two-dimensional Hubbard model, which conceptualizes the materials as electrons moving across a quantum chessboard. This model has now been shown to effectively capture the essential features of cuprate superconductivity.

"The idea in physics is to keep the model as simple as possible because it's difficult enough on its own," said study co-author Ulrich Schollwock, a professor at the University of Munich. The researchers enhanced the model by allowing electrons to make diagonal moves, akin to bishops in chess, and conducted extensive simulations that aligned closely with experimental observations of cuprates.

Historically, superconductivity was believed to occur at extremely low temperatures necessitating the use of liquid helium. The discovery of cuprates in the mid-1980s, which remain superconductive at higher temperatures achievable with cheaper liquid nitrogen, was a significant shock to the scientific community.

Steven White, a professor at the University of California, Irvine and study co-author, commented on the complexity added by quantum mechanics in the Hubbard model. "Although the Hubbard model can be written down as an equation taking only a line or two of text, because it is applied to hundreds of atoms interacting through the strange laws of quantum mechanics, one could simulate it on a computer as large as the earth for thousands of years and still not be able to get the right answers," he said.

This study represents a key advance not only in understanding high-temperature superconductivity but also in utilizing traditional computation methods to tackle quantum mechanical problems, proving that significant progress can still be made without waiting for quantum computing technologies.

Research Report:Coexistence of superconductivity with partially filled stripes in the Hubbard model

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