Physicists at the University of Illinois Urbana-Champaign’s Grainger College of Engineering have discovered unique superconducting behavior in uranium ditelluride, revealing that Cooper pairs—paired electrons responsible for superconductivity—can form uneven patterns even outside the material’s main superconducting state. These patterns, known as pair density waves (PDWs), were previously theorized but not directly observed.
This research, published in the Proceedings of the National Academy of Sciences, presents the first evidence of PDWs in uranium ditelluride persisting in its “ordinary” phase. The study’s lead authors, Eduardo Fradkin and Vidya Madhavan, emphasized the significance of their findings, highlighting that these PDWs can exist above the temperature at which superconductivity vanishes.
Superconductivity allows certain metals to conduct electricity without resistance at low temperatures, emerging from electron interactions that defy conventional rules of particle behavior. Traditional BCS theory describes how electrons form Cooper pairs that act collectively, but unconventional superconductors like uranium ditelluride challenge these principles.
Fradkin’s earlier proposal indicated the potential for PDWs to survive above critical temperatures, suggesting that Cooper pairs could form even without a full superconducting state. The researchers used advanced techniques to create high-quality samples of uranium ditelluride, allowing them to observe the PDWs under varying temperature and magnetic field conditions.
Their findings revealed that some modes persisted even beyond the critical temperature, contradicting simple charge density wave (CDW) explanations and supporting the theory of PDWs. While STM imaging is limited to surface analysis, the consistent results across various methods provide strong evidence of the intriguing behaviors within uranium ditelluride, opening avenues for future research on unconventional superconductivity.
