Higher-charge superconductivity and time-reversal symmetry breaking in kagome superconductors

The condensation of charge-2e Cooper pairs with the quantized magnetic flux in units of h/2e has remained the origin and character of all superconductivity, as described by the BCS theory. We experimentally discovered charge-6e superconductivity in ultrathin kagome superconductor CsV₃Sb₅ ring devices [1], evidenced by the observation of the quantized magnetic flux in units of h/6e in systematic magneto-transport measurements. More recently, we have fabricated new micron-sized CsV₃Sb₅ ring devices with relatively sharp superconducting transition (the onset transition temperature ∼ 3.76 K and the zero-resistance transition temperature ∼ 2.80 K), and strikingly clear charge-6e oscillations are observed, highlighting the robustness of the exotic phase-coherent higher-charge states. Our observations provide ground work for exploring the physical properties of the charge-6e superconductivity as unprecedented phases of matter beyond the condensation of charge-2e Cooper pairs described by the BCS theory. For better understanding on the observed higher-charge superconductivity in our CsV₃Sb₅ devices, we further studied the nonreciprocal property of our CsV₃Sb₅ nanodevices. The field-free superconducting diode effect was observed in the CsV₃Sb₅ flake and micro-bridge devices [2], offering direct evidence for time-reversal symmetry breaking in the superconducting state.

Reference

[1] Jun Ge et al. Physical Review X 14, 021025 (2024) (arXiv: 2201.10352).

[2] Jun Ge et al. arXiv:2506.04601.