A hidden magnetic order could unlock superconductivity

The discovery came from experiments using a quantum simulator cooled to temperatures just above absolute zero. As the system cooled, the researchers observed a consistent pattern in how electrons influence the magnetic orientation of nearby electrons. Since electrons can have spin up or down, these interactions shape the material's overall behavior. The work represents an important step toward explaining unconventional superconductivity and was made possible through a collaboration between experimental physicists at the Max Planck Institute of Quantum Optics in Germany and theorists, including Antoine Georges, director of the Center for Computational Quantum Physics (CCQ) at the Simons Foundation's Flatiron Institute in New York City.

The international team reported its findings in the Proceedings of the National Academy of Sciences.

Why Superconductivity Remains a Puzzle

Superconductivity has been studied for decades because of its potential to transform technologies such as long-distance power transmission and quantum computing. Despite this effort, scientists still lack a complete understanding of how superconductivity arises, especially in materials that operate at relatively high temperatures.

In many high-temperature superconductors, the superconducting state does not emerge directly from an ordinary metallic phase. Instead, the material first passes through an intermediate stage known as the pseudogap. During this phase, electrons behave in unusual ways, and fewer electronic states are available for current to flow. Because of this, understanding the pseudogap is widely seen as essential for uncovering the mechanisms behind superconductivity and improving material performance.

Magnetism Under Pressure From Doping

When a material contains the normal number of electrons, those electrons tend to organize into a well-ordered magnetic pattern called antiferromagnetism. In this arrangement, neighboring electron spins point in opposite directions, much like a carefully synchronized left right sequence.

This orderly pattern breaks down when electrons are removed through a process known as doping. For many years, scientists believed that doping completely eliminated long-range magnetic order. The new PNAS study challenges that assumption by showing that at extremely low temperatures, a subtle form of organization survives beneath the apparent disorder. These experiments were guided by earlier theoretical work on the pseudogap carried out at the CCQ, which led to a 2024 paper in Science.

Simulating Quantum Matter With Ultracold Atoms

To explore this behavior, the research team used the Fermi-Hubbard model, a widely accepted theoretical framework that describes how electrons interact within a solid. Rather than studying actual materials, the researchers recreated the model using lithium atoms cooled to billionths of a degree above absolute zero. These atoms were arranged in a carefully controlled optical lattice created with laser light.

Ultracold atom quantum simulators allow scientists to reproduce complex material behavior under conditions that traditional solid-state experiments cannot achieve. Using a quantum gas microscope, which can image individual atoms and detect their magnetic orientation, the team collected more than 35,000 detailed snapshots. These images captured both the positions of atoms and their magnetic correlations across a broad range of temperatures and doping levels.

"It is remarkable that quantum analog simulators based on ultracold atoms can now be cooled down to temperatures where intricate quantum collective phenomena show up," says Georges.

A Universal Magnetic Pattern Emerges

The data revealed a striking result. "Magnetic correlations follow a single universal pattern when plotted against a specific temperature scale," explains lead author Thomas Chalopin of the Max Planck Institute of Quantum Optics. "And this scale is comparable to the pseudogap temperature, the point at which the pseudogap emerges." This means the pseudogap is closely tied to subtle magnetic structures that persist beneath what initially appears to be disorder.

The study also showed that electron interactions in this regime are more complex than simple pairings. Instead, electrons form larger, multiparticle correlated structures. Even a single dopant can disrupt magnetic order across a surprisingly wide area. Unlike earlier research that focused only on pairs of electrons, this study measured correlations involving up to five particles at once, a level of detail achieved by only a small number of laboratories worldwide.

Revealing Hidden Correlations

For theorists, these findings provide an important new benchmark for models of the pseudogap. More broadly, the results bring scientists closer to understanding how high-temperature superconductivity emerges from the collective motion of interacting, dancing electrons. "By revealing the hidden magnetic order in the pseudogap, we are uncovering one of the mechanisms that may ultimately be related to superconductivity," Chalopin explains.

The work also highlights the importance of close cooperation between theory and experiment. By combining precise theoretical predictions with carefully controlled quantum simulations, the researchers were able to uncover patterns that would otherwise remain hidden.

This international effort brought together experimental and theoretical expertise, and future experiments aim to cool the system even further, search for additional forms of order, and develop new ways to observe quantum matter from fresh perspectives.

"Analog quantum simulations are entering a new and exciting stage, which challenges the classical algorithms that we develop at CCQ," says Georges. "At the same time, those experiments require guidance from theory and classical simulations. Collaboration between theorists and experimentalists is more important than ever."