Pair-density waves found in uranium ditelluride — ScienceAlert

A research group led by scientists at the University of Illinois Urbana-Champaign has found compelling evidence of pair-density waves on the surface of uranium ditelluride. These structures persisted at temperatures higher than the superconducting transition temperature, ScienceAlert reports. The results were published in the journal PNAS.

Electron pairs form patterns

In the superconducting state, electrons can form Cooper pairs and move through a material without electrical resistance or energy loss through heating. The existence of pair-density waves, or PDWs, was theoretically predicted as early as 2007. In this state, Cooper pairs form spatially repeating patterns resembling waves in sand.

Uranium ditelluride enters a superconducting state at temperatures below approximately 2.1 kelvin, or about minus 271 degrees Celsius. The material also interests physicists as a possible rare spin-triplet superconductor: in such a system, paired electrons also have a small magnetic orientation.

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Observations of magnetic field and temperature

Signs of PDW had previously been recorded in uranium ditelluride. In the new study, the scientists used a high-quality sample of the material and a vector magnetic scanning tunneling microscope. The instrument makes it possible to measure magnetic responses for different field directions.

The team systematically varied the temperature, strength and direction of the magnetic field, tracking the evolution of the detected modes. To explain the charge patterns below the critical temperature and far above it, the researchers also used theoretical models.

The persistence of these modes above the temperature at which superconductivity disappears does not mean that uranium ditelluride retains bulk superconductivity at higher temperatures. At the same time, the observation helps investigate how Cooper pairs can exist outside the conventional superconducting state. The scientists also stress the need to clarify the relationship between pair-density waves and charge-density waves, in which electrons form nonuniform spatial structures.