Physicists at the University of Illinois Urbana-Champaign's Grainger College of Engineering have uncovered evidence of an unusual form of superconducting behavior in uranium ditelluride. Their experiments show that Cooper pairs, the paired electrons that make superconductivity possible, can arrange themselves into uneven patterns even when the material is no longer in its main superconducting state.
These patterns are called pair density waves (PDWs). Scientists first predicted them about 20 years ago, and previous studies have observed them alongside superconductivity in other metals. The new research, published in the Proceedings of the National Academy of Sciences, goes further. It provides the first direct evidence that PDWs in uranium ditelluride can remain in the material's "ordinary" phase after superconductivity has disappeared.
"Pair density waves are the Cheshire Cat's grin of superconductivity," said Eduardo Fradkin, an Illinois Grainger Engineering physics professor and a project co-lead. "They are the vestige that remains once the phase itself has disappeared. In conventional superconductors, Cooper pairs form when the full phase transition occurs, but, in this system, their observation in PDWs above the transition point shows that they are formed beforehand in a different state."
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