This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Unconventional superconductors can host unusual electronic states, but understanding what drives their superconductivity becomes difficult when different forms of order coexist. The kagome metal CsV3Sb5 has become a particularly debated example.
It develops charge density wave order at about 94 K before becoming superconducting at about 2.5 K, yet experiments have offered conflicting views of whether its superconducting gap is conventional or contains nodes. Resolving this question is important because knowing how superconductivity forms can guide the search for better superconducting materials. Addressing this challenge, a research team led by associate professor Shinji Kawasaki, working with professor Guo-qing Zheng, investigated CsV3Sb5 using in situ uniaxial strain and nuclear quadrupole resonance measurements.
Both researchers are from the Department of Physics at Okayama University in Japan. High-quality single crystals were strained along one crystallographic direction using a custom piezoelectrically driven strain cell, while the researchers monitored the superconducting transition and local electronic properties. The study was published in the journal Physical Review Letters on Aug. 28, 2026.
The team found that stretching the crystal, rather than compressing it, substantially increased the superconducting transition temperature. At zero strain, the transition began at about 3.0 K, while tensile strain of +0.90% raised it to 3.6 K. The charge density wave remained essentially unchanged under strain, showing that superconductivity could be tuned independently of the material's existing charge order.
This decoupling offers researchers a new way to study the two phenomena separately. A closer look at the superconducting state revealed an even more striking result. Under the largest tensile strain, the material underwent two superconducting transitions.
The first occurred at 3.6 K and was associated with a nodal superconducting state, while a second transition appeared at 3.0 K and showed a nodeless state. The findings indicate that two distinct superconducting states, which are nearly degenerate under ambient conditions, can separate when strain is applied, helping explain why previous experiments reached different conclusions about the material's superconducting nature. "For years, different measurements of CsV3Sb5 have pointed toward seemingly different superconducting states," says Kawasaki.
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