Pair density waves observed above superconducting temperature for first time

Physicists confirm exotic electron state in uranium ditelluride, opening new path to understanding high-temperature superconductivity

By LineZotpaper

Published19 October 2026

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A team led by researchers from the University of Illinois at Urbana-Champaign has found compelling evidence of pair density waves (PDWs) on the surface of uranium ditelluride, a metal that becomes superconducting at very low temperatures. In an unexpected twist, the PDWs persisted at temperatures above the material's superconducting transition point, a phenomenon never before observed. The results, published in PNAS, confirm a theoretical prediction from 2007 and could help scientists understand how Cooper pairs form in unconventional superconductors, bringing the goal of higher-temperature superconductivity closer.

Superconductors conduct electricity with zero resistance, a property that could transform computing, energy grids, and transport. But superconductivity typically requires extremely cold temperatures, limiting its practical use. In conventional superconductors, free electrons pair into Cooper pairs at the critical temperature and condense into a low-energy quantum state.

Back in 2007, scientists predicted a more exotic form of electron movement, called a pair density wave (PDW), in which Cooper pairs move in ripple-like patterns. Now, using a custom-made high-quality sample of uranium ditelluride and a vector magnetic field scanning tunneling microscope (STM), the team has detected clear signatures of PDWs. "PDWs are the Cheshire Cat's grin of superconductivity," said physicist Eduardo Fradkin. "They are the vestige that remains once the phase itself has disappeared."

The crucial advance: the PDWs were observed not only below the critical temperature of about 2.1 Kelvin but also at temperatures significantly above it. "We even showed that the modes persist above the temperature at which superconductivity disappears, a tell-tale theoretical prediction that has not been convincingly observed before now," said physicist Vidya Madhavan.

The researchers combined experimental data with theoretical models to confirm the patterns were intrinsic. "Thanks to new methods for growing higher-quality samples, we were able to observe spectral signatures that respond to temperature and magnetic fields exactly as pair density waves should," Madhavan added.

This does not mean bulk superconductivity occurs at higher temperatures in this material, but it demonstrates that Cooper pairs can exist outside the full superconducting state, potentially offering clues to designing superconductors that work at more practical temperatures.

Physicist Julian May-Mann from Stanford University noted the difficulty of identifying PDWs. "Confirming the existence of a PDW requires both high-quality experimental data as well as careful theoretical analysis," he said. Understanding how PDWs relate to charge density waves will be central to future experimental interpretation.

Analysis

Why This Matters

The discovery provides direct evidence that Cooper pairs can form and exist outside the full superconducting phase, challenging the traditional understanding of how superconductivity begins.
Understanding pair density waves could be key to designing materials that superconduct at higher temperatures, potentially making technologies like lossless power transmission and magnetic levitation far more practical.
The findings validate a theoretical framework that has awaited experimental confirmation for nearly two decades, giving condensed matter physics a solid foundation for further work.

Background

Superconductivity occurs when electrons join into Cooper pairs and travel through a material with no electrical resistance. This usually happens only at very low temperatures and is explained by conventional theory for many materials. Uranium ditelluride is a rare 'spin-triplet' superconductor, where paired electrons also carry a magnetic orientation. In 2007, theorists proposed that in certain materials, Cooper pairs could form periodic patterns called pair density waves. Until now, those waves had been seen only in hints and never above the superconducting transition point. Charge density waves, where single electrons form patterns, are a related but distinct phenomenon.

Key Perspectives

Research Team (University of Illinois): The observation of PDWs above the critical temperature is a breakthrough that confirms a longstanding theoretical prediction. The new sample quality and vector-magnet STM were essential to distinguishing the effect from other phenomena. The team views this as a step toward understanding the fundamental physics that could eventually enable higher-temperature superconductors.

Julian May-Mann (Stanford University): Emphasises that PDWs are tricky to analyse in real materials because they can mimic conventional superconductivity or charge density waves in different experiments. Confirmation requires exceptional data quality and careful theoretical modelling, both of which this study provides.

Cautious interpretation: The discovery does not mean higher-temperature superconductivity has been achieved, but it opens a new window into the pre-condensation behavior of Cooper pairs.

What to Watch

Whether similar PDW signatures can be found in other superconducting materials, especially those that already show promise for higher transition temperatures.
The interplay between PDWs and charge density waves; resolving their relationship will be essential for correctly interpreting future experiments.
Follow-up studies by other groups to independently replicate the observation and test whether the effect can be enhanced or stabilised with different sample preparation or external conditions.

Sources

New Form of Superconductor Behavior Discovered That We've Never Seen Before · ScienceAlert

Checked

9 claims in this story checked against 1 source: 3 supported.

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Partly supportedHeadline: PDWs were observed above the superconducting temperature 'for first time'.ScienceAlert: “has not been convincingly observed before now”
Partly supportedSummary: 'Physicists confirm' the exotic electron state in uranium ditelluride.ScienceAlert: “has found compelling evidence of PDWs on the surface of the metal uranium ditelluride”
Partly supportedThe results 'confirm a theoretical prediction from 2007' and could help explain how Cooper pairs form in unconventional superconductors, 'bringing the goal of higher-temperature superconductivity closer'.ScienceAlert: “This doesn't mean bulk superconductivity is happening in uranium ditelluride at higher temperatures, but it does help physicists understand how Cooper pairs function and how they can exist outside of the conventional superconducting state. It could also help researchers better understand the physics needed to develop superconductors at higher temperatures.”
Partly supportedFradkin: 'PDWs are the Cheshire Cat's grin of superconductivity,'ScienceAlert: “Pair density waves are the Cheshire Cat's grin of superconductivity”
SupportedMadhavan: 'We even showed that the modes persist above the temperature at which superconductivity disappears, a tell-tale theoretical prediction that has not been convincingly observed before now.'ScienceAlert: “We even showed that the modes persist above the temperature at which superconductivity disappears, a tell-tale theoretical prediction that has not been convincingly observed before now," says physicist Vidya Madhavan”
Partly supportedThe researchers combined experimental data with theoretical models 'to confirm the patterns were intrinsic'.ScienceAlert: “By systematically varying both the magnitude and direction of the field, together with temperature, we could track how these modes evolved and build confidence that the behavior we observed was intrinsic.”
SupportedUranium ditelluride becomes superconducting at about 2.1 Kelvin.ScienceAlert: “Uranium ditelluride becomes a superconductor below about 2.1 Kelvin”
SupportedMay-Mann: 'Confirming the existence of a PDW requires both high-quality experimental data as well as careful theoretical analysis.'ScienceAlert: “Confirming the existence of a PDW requires both high-quality experimental data as well as careful theoretical analysis.”
Partly supportedThe PDW phenomenon was 'never before observed' (a first, stated without hedge in the body).ScienceAlert: “something that's never been seen before”