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 the electrons affected the magnetic orientation of nearby electrons. Because electrons can spin up or down, these interactions shape the overall behavior of the material. The work represents an important step toward explaining unconventional superconductivity and was made possible by a collaboration between experimental physicists at the Max Planck Institute for 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.

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

Why superconductivity remains a mystery

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

For many high-temperature superconductors, the superconducting state does not arise directly from the ordinary metal phase. Instead, the material first passes through a transition stage known as a pseudogap. During this phase, the electrons behave in unusual ways and fewer electronic states are available for flow. For this reason, understanding the pseudogap is widely regarded as crucial to uncovering the mechanisms behind superconductivity and improving material performance.

Magnetism under pressure from doping

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

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

Simulation of quantum matter with ultracold atoms

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

Quantum simulators of ultracold atoms allow scientists to reproduce the complex behavior of a material 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 images. These images captured both the positions of the atoms and their magnetic correlations over a wide range of temperatures and doping levels.

“Remarkably, quantum analog simulators based on ultracold atoms can now be cooled to temperatures at which complex quantum collective phenomena manifest,” says Georges.

A universal magnetic pattern appears

The data revealed a surprising 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 appears.” This means that the pseudogap is intimately tied to the fine magnetic structures that persist beneath what initially appears to be clutter.

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

Revealing hidden correlations

For theorists, these findings represent an important new standard for pseudogap models. More generally, the results bring scientists closer to understanding how high-temperature superconductivity arises from the collective motion of interacting dancing electrons. “By revealing the hidden magnetic order in the pseudogap, we reveal one of the mechanisms that may ultimately be related to superconductivity,” explains Chalopin.

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

This international effort brought together experimental and theoretical knowledge, and future experiments aim to further cool the system, search for other forms of order, and develop new ways of observing quantum matter from new perspectives.

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