Researchers have uncovered and explained an unusual form of superconductivity that only appears under extremely strong magnetic fields. The work, led in part by Rice University physicist Andriy Nevidomskyy, was published in Science and describes how uranium ditelluride (UTe2) forms a distinctive superconducting halo when exposed to intense magnetic conditions.
Under normal circumstances, magnetic fields disrupt superconductors. Even relatively modest fields tend to weaken superconductivity, while stronger ones usually eliminate it entirely once a critical limit is reached. UTe2 breaks this rule. In 2019, scientists discovered that it can remain superconducting in magnetic fields hundreds of times stronger than what typical materials can withstand.
“When I first saw the experimental data, I was stunned,” said Nevidomskyy, a member of the Rice Advanced Materials Institute and the Rice Center for Quantum Materials. “The superconductivity was first suppressed by the magnetic field as expected but then reemerged in higher fields and only for what appeared to be a narrow field direction. There was no immediate explanation for this puzzling behavior.”
A Superconducting “Resurrection” at Extreme Fields
This strange behavior, first observed by teams at the University of Maryland (UMD) and the National Institute of Standards and Technology (NIST), quickly drew attention across the physics community. In UTe2, superconductivity disappears below 10 Tesla, which is already an extremely strong field, but unexpectedly returns at field strengths above 40 Tesla.
Scientists have named this revival the Lazarus phase. It turns out that this phase depends strongly on the angle between the magnetic field and the material’s crystal structure.
Working with collaborators at UMD and NIST, Nevidomskyy helped map how this high-field superconductivity changes with direction. Their measurements showed that the superconducting region forms a toroidal, or doughnutlike, shape that surrounds a particular axis within the crystal.
“Our measurements revealed a three-dimensional superconducting halo that wraps around the hard b-axis of the crystal,” said Sylvia Lewin of NIST, a co-lead author on the study. “This was a surprising and beautiful result.”
Building a Model to Explain the Halo
To understand what was happening, Nevidomskyy created a theoretical model that could explain the observations without depending heavily on uncertain microscopic details. The model uses a phenomenological approach, focusing on the overall behavior rather than the exact underlying mechanisms that cause electrons to pair into Cooper pairs.
The results matched the experimental data closely, especially the unusual way superconductivity changes with the direction of the magnetic field. The model shows how orientation plays a crucial role in whether superconductivity survives or returns in UTe2.
How Magnetism and Superconductivity Interact
The study also revealed that Cooper pairs in this material behave as if they carry angular momentum, similar to a spinning object. When a magnetic field is applied, it interacts with this motion, creating a directional effect that produces the observed halo pattern.
This insight helps explain how magnetism and superconductivity can coexist in materials with strong directional properties like UTe2.
“One of the experimental observations is the sudden increase in the sample magnetization, what we call a metamagnetic transition,” said NIST’s Peter Czajka, co-lead author on the study. “The high-field superconductivity only appears once the field magnitude has reached this value, itself highly angle-dependent.”
Scientists are still debating what causes this metamagnetic transition and how it influences superconductivity. Nevidomskyy said the new model could help clarify this open question.
“While the nature of the pairing glue in this material remains to be understood, knowing that the Cooper pairs carry a magnetic moment is a key outcome of this study and should help guide future investigations,” he said.
Research Team and Support
The study involved Corey Frank and Nicholas Butch from NIST; Hyeok Yoon, Yun Suk Eo, Johnpierre Paglione and Gicela Saucedo Salas from UMD; and G. Timothy Noe and John Singleton from Los Alamos National Laboratory. Funding was provided by the U.S. Department of Energy and the National Science Foundation.