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Spinning or not spinning? Experts discuss controversies of Srâ‚‚RuOâ‚„'s unusual superconductivity

Superconductors can carry electricity without losing energy, a superpower that makes them invaluable for a range of sought-after applications, from maglev trains to quantum computers. Generally, this comes at the price of having to keep them extremely cold, an opportunity cost that has frequently hindered widespread use.

Understanding of how superconductors work has also progressed, but there still remains a great deal about them that is unknown. For example, among many materials known to have superconducting properties, some do not behave according to conventional theory.

One such puzzling material is strontium ruthenate or Sr₂RuO₄, which has challenged scientists since it was discovered to be a superconductor in 1994. Initially, researchers thought this material had a special type of superconductivity called a "spin-triplet" state, which is notable for its spin supercurrent. But even after considerable investigation, a full understanding of its behavior has remained a mystery.

Recently, new data has suggested that strontium ruthenate might act more like a "spin-singlet" state, where the electron pairs have no spin. Changes in material properties when pressure is applied also point to a unique kind of behavior. However, a full explanation of what is happening has still eluded scientists, and several research steps are still necessary to open the "Gate of Truth" of superconductivity in this material.

In a new appearing in Nature Â鶹ÒùÔºics, a team from Kyoto University highlights several ongoing controversies in the field, in particular the discrepancies between experiments using uniaxial pressure and ultrasound, a point that is likely to surprise many in the research community.

"Our study points to the urgent need for further investigation and rethinking of traditional ideas about superconductivity," explains Giordano Mattoni, a contributor to the article. "New forms of exotic electron pairing could be hiding in the superconducting state of strontium ruthenate, like the novel inter-orbital spin-triplet state that behaves like a spin-singlet state."

Understanding these mysteries could help explain more about superconductivity in general, helping in the search for new materials that could be used in future advanced technologies.