Direct observation of orbital-selective anisotropic Cooper pairing in Kagome superconductor CsV₃Sb₅

Kagome materials are known for their unique electronic structures and strong geometric frustration, arising from an unusual lattice consisting of corner-shared triangles. The superconductivity in a Kagome system is theoretically predicted to exhibit the exotic chiral properties, garnering significant attention. Recently, Kagome metals AV₃Sb₅ (A = K, Rb, and Cs), which feature a Kagome lattice formed by V atoms, are discovered to exhibit superconductivity intertwined with an unconventional charge density wave (CDW) that breaks time-reversal symmetry. Despite the extensive studies, the pairing symmetry remains elusive owing to the lack of direct measurements of the superconducting gap in the momentum space, hindering a microscopic understanding of the intertwined ground state of AV₃Sb₅. In this presentation, we will report the superconducting gap structure in the momentum space of CsV₃Sb₅ directly measured by low-temperature and high-resolution laser-based angle-resolved photoemission spectroscopy. Our findings reveal a highly anisotropic superconducting gap on the Fermi surface (FS) derived from the V 3d orbitals and an isotropic gap on the FS derived from the Sb 5p orbitals. Based on these key observations, the fundamental implications on the pairing mechanism of Kagome superconductors will be discussed.