30-Year Superconductivity Mystery Shifts as New Strain Tests Challenge Old Theories

Superconductors carry electricity with zero resistance. However, this behavior usually appears only at very low temperatures. Strontium ruthenate, known as Sr₂RuO₄, has puzzled scientists since 1994. Despite decades of research, its superconducting behavior stayed unclear. Researchers consider this material unusually pure. Even so, its internal pairing mechanism remained debated.

Symmetry Matters

Superconductivity depends on how electrons pair together. Therefore, symmetry plays a crucial role in explaining the process. Many theories suggested a complex, two-component pairing state. Such states can create internal magnetic effects or multiple regions. However, scientists needed stronger evidence. That gap motivated a fresh experimental approach. Applying strain can reveal hidden superconducting properties. For example, stretching or twisting a crystal often shifts its transition temperature. Earlier ultrasound studies hinted at strong shear sensitivity. As a result, many researchers favored a two-component explanation. A true two-component state should react strongly to shear strain. That expectation guided the next experiment.

A New Shear Strain Experiment

A Kyoto University team tested ultrathin Sr₂RuO₄ crystals. They applied three controlled types of shear strain. The team measured changes using high-resolution optical tools. They worked at temperatures as low as 30 Kelvin. Surprisingly, the superconducting temperature barely moved.
Any change stayed below measurable limits.
Results Mean.
Shear strain showed almost no effect on superconductivity. Therefore, several popular theories no longer fit. The findings point toward a simpler, one-component state. Alternatively, an entirely new superconducting state may exist. “This work brings us closer to solving a decades-old mystery,” said lead author Giordano Mattoni.

Open Questions and Future Impact

A contradiction still remains. Earlier ultrasound results showed strong shear effects. Understanding this mismatch is now a key challenge. However, the new method has wider value. Researchers can apply this strain technique to other materials. As a result, it may unlock more hidden quantum behaviors.