“Finding the upper critical field, ie the value of magnetic field that suppresses superconductivity, is important for establishing that the type of superconductivity in uranium ditelluride is exotic, what we call spin-triplet, or involving electrons having aligned spins”Nicholas Butch
Researchers have discerned a rare phenomenon known as re-entrant superconductivity in a uranium-based compound, unconventional behavior that could lead to the material’s use in quantum computing. Uranium ditelluride, whose physical properties were thought to be of little interest, was shown to display “Lazarus superconductivity” – named after the biblical figure that rose from the dead four days after being buried – as the phenomenon happens when a superconducting state occurs, breaks down, and then re-emerges in a material because of a change in a parameter.
In superconductivity electrons travel through a material with perfect efficiency, but with Lazarus superconductivity strong magnetic fields tend to destroy the superconducting state in most materials. As reported in Nature Physics [Ran et al. Nat. Phys. (2019) DOI: 10.1038/s41567-019-0670-x], however, a team from the University of Maryland, the National Institute of Standards and Technology, the National High Magnetic Field Laboratory and the University of Oxford, in researching the relationship between magnetism and strong electronic interactions in uranium compounds, observed superconductivity to arise in uranium ditelluride, before disappearing and then returning under the influence of a very strong magnetic field.
The finding follows recent reporting by the team of the rare ground state in the material called “spin-triplet superconductivity”, where pairs of electrons are aligned in the same direction rather than in opposite directions, which magnetic fields can more easily disrupt, destroying superconductivity. All measurements suggest that uranium ditelluride is a useful spin-triplet superconductor, and shows signs of being a topological superconductor in the same way as other spin-triplet superconductors, indicating that it could be an accurate component for fault-tolerant quantum computing.
Spin-triplet superconductors can withstand much higher magnetic fields, and a combination of very high-field magnets and improved instrumentation helped the team push uranium ditelluride even further. They tested it in some of the highest magnetic fields available to identify the upper limit at which the magnetic fields broke down the material's superconductivity. Rather than destroying superconductivity, high magnetic fields seemed to stabilize it, and although it is not obvious what is happening at the atomic level, evidence points to a phenomenon fundamentally different than anything previously observed.
As team leader Nicholas Butch told Materials Today, “Finding the upper critical field, ie the value of magnetic field that suppresses superconductivity, is important for establishing that the type of superconductivity in uranium ditelluride is exotic, what we call spin-triplet, or involving electrons having aligned spins”. Further experimentation will be needed to identify the precise nature of the superconductivity, or multiple types of superconductivity, in uranium ditelluride, and the researchers also want to examine the effects of magnetic fields and applied pressure, which dramatically affect superconductivity.