Physicists have observed a rare phenomenon called re-entrant superconductivity in uranium ditelluride (UTe2). The discovery, reported in the journal Nature Physics, furthers the case for uranium ditelluride as a promising material for use in quantum computers.
Ran et al observed re-entrant superconductivity in uranium ditelluride. Image credit: Emily Edwards / JQI.
Superconductivity is a state in which electrons travel through a material with perfect efficiency. By contrast, copper — which is second only to silver in terms of its ability to conduct electrons — loses roughly 20% power over long-distance transmission lines, as the electrons bump around within the material during travel.
Re-entrant superconductivity, nicknamed Lazarus superconductivity after the Biblical character, is especially strange, because strong magnetic fields usually destroy the superconducting state in the vast majority of materials.
In uranium ditelluride, however, a strong magnetic field coupled with specific experimental conditions caused Lazarus superconductivity to arise not just once, but twice.
“This is indeed a remarkable material and it’s keeping us very busy,” said co-author Professor Johnpierre Paglione, from the University of Maryland and the NIST Center for Neutron Research.
“Uranium ditelluride may very well become the ‘textbook’ spin-triplet superconductor that people have been seeking for dozens of years and it likely has more surprises in store.”
In an earlier paper, Professor Paglione and colleagues reported that uranium ditelluride’s superconductivity involved unusual electron configurations called spin triplets, in which pairs of electrons are aligned in the same direction.
In the vast majority of superconductors, the orientations — called spins — of paired electrons point in opposite directions.
These pairs are called singlets. Magnetic fields can more easily disrupt singlets, killing superconductivity.
Spin triplet superconductors, however, can withstand much higher magnetic fields.
In the new study, the scientists tested uranium ditelluride in some of the highest magnetic fields available.
By exposing the material to magnetic fields up to 65 T (teslas), they attempted to find the upper limit at which the magnetic fields crushed the material’s superconductivity.
They also experimented with orienting the uranium ditelluride crystal at several different angles in relation to the direction of the magnetic field.
At about 16 T, the material’s superconducting state abruptly changed.
While it died in most of the experiments, it persisted when the crystal was aligned at a very specific angle in relation to the magnetic field. This unusual behavior continued until about 35 T, at which point all superconductivity vanished and the electrons shifted their alignment, entering a new magnetic phase.
As the researchers increased the magnetic field while continuing to experiment with angles, they found that a different orientation of the crystal yielded yet another superconducting phase that persisted to at least 65 T, the maximum field strength the team tested.
It was a record-busting performance for a superconductor and marked the first time two field-induced superconducting phases have been found in the same compound.
Instead of killing superconductivity in uranium ditelluride, high magnetic fields appeared to stabilize it.
“While it is not yet clear exactly what is happening at the atomic level, the evidence points to a phenomenon fundamentally different than anything scientists have seen to date,” said Dr. Nicholas Butch, from the University of Maryland and the NIST Center for Neutron Research.
“On top of its convention-defying physics, uranium ditelluride shows every sign of being a topological superconductor, as are other spin-triplet superconductors. Its topological properties suggest it could be a particularly accurate and robust component in the quantum computers of the future.”
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Sheng Ran et al. Extreme magnetic field-boosted superconductivity. Nature Physics, published online October 7, 2019; doi: 10.1038/s41567-019-0670-x
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