Stretching kagome metal CsV3Sb5 separates two superconducting states, study reports

The kagome metal CsV3Sb5 develops charge density wave order (a wave-like pattern in its electrons) at about 94 K, then becomes superconducting at about 2.5 K, according to a Phys.org report. Experiments on the material have offered conflicting views of whether its superconducting gap is conventional or contains nodes, the report stated. Knowing how superconductivity forms can guide the search for better superconducting materials, according to the report.

A research team led by associate professor Shinji Kawasaki, working with professor Guo-qing Zheng, investigated CsV3Sb5 using in situ uniaxial strain (stretching along one crystal direction) and nuclear quadrupole resonance measurements, Phys.org reported. Both researchers are from the Department of Physics at Okayama University in Japan. The study was published in the journal Physical Review Letters on 28 August 2026, according to the report.

The researchers strained high-quality single crystals along one crystallographic direction using a custom piezoelectrically driven strain cell, while monitoring the superconducting transition and local electronic properties, according to the report. They 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, and tensile strain of +0.90% raised it to 3.6 K. The charge density wave remained essentially unchanged under strain, which the report said showed superconductivity could be tuned independently of the material's existing charge order.

Under the largest tensile strain, the material underwent two superconducting transitions, according to the report. The first occurred at 3.6 K and was associated with a nodal superconducting state (one whose superconducting gap drops to zero in certain directions), 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 (close in energy) under ambient conditions, can separate when strain is applied, helping explain why previous experiments reached different conclusions, the report stated.

"For years, different measurements of CsV3Sb5 have pointed toward seemingly different superconducting states," Kawasaki said. "Our results show that these states can coexist and that uniaxial strain can separate them, giving us a direct way to study each state." Kawasaki also said: "Strain gives us an independent control knob in this material—it enhances superconductivity without changing the bulk charge density wave."

The researchers further found that the unconventional nodal component becomes stronger under tensile strain, increasing from a contribution of 10% at zero strain to about 26% at +0.90% strain, according to the report. The report stated that hydrostatic pressure changes superconductivity largely through its effect on charge order, while the results show uniaxial strain can selectively strengthen a superconducting pairing channel while leaving the competing background state robust. The report said the approach could be useful beyond CsV3Sb5.