Unconventional Superconductivity in Kagome Lattice Superconductors

The kagome superconductor AV3Sb5 (A = K, Cs, Rb) exhibits unconventional charge-density-wave (CDW) order with broken time-reversal and rotational symmetries. However, the superconducting symmetry remains unclear. We investigate the superconducting state of CsV3Sb5 by studying impurity effects through electron irradiation and magnetic penetration depth measurements. We found that non-magnetic impurities change from an anisotropic superconducting gap to an isotropic one without inducing a nodal state. Furthermore, transport measurements under high pressure show that the double superconducting dome persists even after introducing impurities. Our results indicate that CsV3Sb5 hosts a non-chiral, anisotropic s-wave superconducting state without sign change of the order parameter both at ambient and under pressure, and supports a new type of unconventional superconductivity due to bond-order fluctuations.