Bad’ and mysterious yet highly effective in superconducting at high temperatures; even if, according to expectations, these materials should not behave like this; new research explains why; reconciling theory and experiments.

In jargon, they are called “bad metals,” but they are not really so bad. As a matter of fact, they are the best superconductors because they are able to conduct current with the highest efficiency and without resistance up to high temperatures. This has been seen experimentally.

Yet their behavior remains a mystery. The repulsive forces between the electrons in these materials are much stronger than in low-temperature superconductors: so how do particles with the same charge overcome these forces and manage to pair-up and to transport current as it happens in “traditional” superconductors?

A team of researchers of SISSA in Trieste in collaboration with the Vienna University of Technology have found a possible, surprising answer.

According to the study published in Physical Review Letters, in these materials the electrons would transform into new “objects,” with an unprecedented character that would allow them to pair up and thereby superconduct the current. In their research, the researchers also demonstrated the peculiarity of a new type of “Bad metals,” called “Hund’s metals,” important for a class of iron-based materials. Scientists believe that these materials are particularly interesting because they are superconductive and rather malleable, which makes them highly suited to technological applications.

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