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Scientists twisted a mysterious superconductor and got a shocking result

A stubborn superconductor just defied expectations again—bringing scientists closer to answers, but also deeper into mystery.

Date:

March 22, 2026

Source:

Kyoto University

Summary:

A decades-old superconducting mystery just took a surprising turn. Strontium ruthenate, a material that conducts electricity with zero resistance at low temperatures, has long puzzled scientists with hints of an exotic, complex superconducting state. But by carefully twisting and distorting ultra-thin crystals, researchers found something unexpected: the material barely reacted at all. This challenges years of assumptions and suggests its behavior may be far simpler—or far stranger—than previously thought.

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FULL STORY

A key experiment found that twisting a mysterious superconductor barely changes its behavior, overturning long-standing theories. The result narrows the possibilities—but also creates a new scientific puzzle. Credit: Shutterstock

Superconductors are materials that allow electricity to flow without resistance, typically only at extremely low temperatures. While most follow well-understood physical rules, strontium ruthenate, Sr2RuO4, has remained difficult to explain since its superconducting behavior was first identified in 1994. It is one of the most precisely studied unconventional superconductors, yet researchers still disagree about how its electrons pair up and what symmetry governs that process.

One way scientists investigate superconductors is by observing how their superconducting transition temperature, known as Tc, responds to strain. Different superconducting states react in distinct ways when a crystal is stretched, compressed, or twisted. Earlier studies, particularly those using ultrasound, suggested that Sr2RuO₄ could host a two-component superconducting state. This more complex form can produce unusual effects such as internal magnetic fields or multiple superconducting regions existing at once. However, such a state is expected to show a strong response to shear strain.

Precision Shear Strain Experiment Reveals Surprise

To explore this further, a research team from Kyoto University designed an experiment focused on applying controlled strain to Sr2RuO4. They developed a method to introduce three different types of shear strain to extremely thin crystals of the material. Shear strain involves shifting parts of a crystal sideways, similar to sliding the top of a deck of cards relative to the bottom. Using high-resolution optical imaging, they measured the strain with precision at temperatures as low as 30 degrees K (−243 degrees C).

The result was unexpected. The superconducting transition temperature barely changed. Any variation in Tc was smaller than 10 millikelvin per percent strain, which is effectively too small to detect with confidence.

Findings Challenge Leading Theories

These observations indicate that shear strain has almost no influence on when Sr2RuO4 becomes superconducting. This outcome rules out several existing theories and places strong limits on the types of superconducting states that remain viable. Instead of supporting a two-component state, the findings point toward a one-component superconducting state or possibly a more unconventional state that has not yet been fully explored.

"Our study represents a major step toward solving one of the longest-standing mysteries in condensed-matter physics," says first author Giordano Mattoni, Toyota Riken -- Kyoto University Research Center.

A New Puzzle Emerges

While the results narrow down the possibilities, they also introduce a new challenge. Previous ultrasound experiments clearly showed a strong response to shear strain, whereas these direct strain measurements show almost none. Explaining this discrepancy is now an important open question for researchers.

Broader Impact Beyond Sr2RuO4

The strain-control approach developed in this work could be useful for studying other superconductors that may have multi-component behavior, including materials such as UPt₃. It may also help scientists better understand systems with complex phase transitions.