The 'Lazarus Phase': How a Mysterious Superconductor Dies and Comes Back to Life

A Superconductor That Refuses to Stay Dead

Physics has a new puzzle on its hands—and it involves a material that seemingly breaks one of the most fundamental rules of superconductivity. Uranium ditelluride (UTe₂) has stunned researchers by exhibiting a form of superconductivity that vanishes under powerful magnetic fields, only to resurrect itself when those fields grow even stronger. Scientists have taken to calling this remarkable phenomenon the "Lazarus phase," and understanding it could reshape our grasp of quantum materials.

The findings, published in the journal Science and led in part by Rice University physicist Andriy Nevidomskyy, reveal that UTe₂ forms a distinctive superconducting region—described as a halo—when subjected to extreme magnetic conditions that would obliterate superconductivity in virtually any other known material.

Breaking the Rules of Conventional Superconductivity

Under ordinary circumstances, superconductors and magnetic fields do not get along. Even relatively mild magnetic exposure tends to weaken a material's ability to conduct electricity with zero resistance, and sufficiently strong fields destroy superconductivity altogether once a critical threshold is crossed.

UTe₂ simply does not follow that playbook. In 2019, scientists first discovered that this unusual compound could sustain superconductivity in magnetic fields hundreds of times more powerful than what conventional superconducting materials can endure. That discovery alone was remarkable. What came next was even more baffling.

Researchers found that in UTe₂, superconductivity initially disappears below 10 Tesla—itself an extraordinarily strong magnetic field—but then, against all expectations, returns at field strengths exceeding 40 Tesla.

"When I first saw the experimental data, I was stunned," said Nevidomskyy, who is affiliated with 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."

Mapping the Superconducting Halo

The Lazarus phase was originally observed by research teams at the University of Maryland (UMD) and the National Institute of Standards and Technology (NIST), and it quickly captured widespread attention throughout the physics community.

Working alongside collaborators at UMD and NIST, Nevidomskyy helped chart precisely how this high-field superconductivity shifts depending on the orientation of the magnetic field relative to the crystal's internal structure. The results were striking: the superconducting zone takes on a toroidal, doughnut-like shape that wraps around a specific 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 Theoretical Framework

To make sense of these observations, Nevidomskyy developed a theoretical model designed to explain the behavior without relying heavily on uncertain microscopic assumptions. Rather than drilling down into the precise mechanisms by which electrons pair up—a process central to all superconductivity—the model takes a broader, phenomenological approach, focusing on the material's overall behavior.

The theoretical predictions aligned closely with experimental measurements, particularly in capturing how dramatically superconductivity changes based on the angle of the applied magnetic field. The model demonstrates that field orientation plays a decisive role in whether superconductivity can survive or re-emerge in UTe₂.

The Magnetic Moment of Cooper Pairs

One of the study's most significant revelations concerns the nature of the electron pairs responsible for superconductivity. In UTe₂, these so-called Cooper pairs appear to carry angular momentum—essentially behaving like tiny spinning objects. When a magnetic field is applied, it interacts with this rotational motion, producing the directional effects that give rise to the observed halo pattern.

This finding sheds new light on how magnetism and superconductivity can coexist in materials with strong directional, or anisotropic, properties.

The research also highlighted the role of a metamagnetic transition—a sudden jump in the material's magnetization that appears to act as a gateway for the Lazarus phase.

"The high-field superconductivity only appears once the field magnitude has reached this value, itself highly angle-dependent," explained NIST's Peter Czajka, co-lead author on the study.

The precise cause of this metamagnetic transition and its relationship to superconductivity remains an open question, though Nevidomskyy believes the new theoretical model offers a valuable starting point for future investigation.

"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 noted.

Why This Discovery Matters

UTe₂'s behavior challenges long-standing assumptions about the limits of superconductivity and opens new avenues for exploring how quantum materials behave under extreme conditions. If scientists can fully decode the mechanisms behind the Lazarus phase, the implications could extend well beyond theoretical physics—potentially informing the development of next-generation superconducting technologies.

The study involved researchers from NIST, the University of Maryland, and Los Alamos National Laboratory, and received funding from the U.S. Department of Energy and the National Science Foundation.