Superconductivity and nematic order in a new titanium-based kagome metal CsTi₃Bi₅ without charge density wave order.

Abstract

The cascade of correlated topological quantum states in the newly discovered vanadium-based kagome superconductors, AV₃Sb₅ (A = K, Rb, and Cs), with a Z₂ topological band structure has sparked immense interest. Here, we report the discovery of superconductivity and electronic nematic order in high-quality single-crystals of a new titanium-based kagome metal, CsTi₃Bi₅, that preserves the translation symmetry, in stark contrast to the charge density wave superconductor AV₃Sb₅. Transport and magnetic susceptibility measurements show superconductivity with an onset superconducting transition temperature T_c of approximately 4.8 K. Using the scanning tunneling microscopy/spectroscopy and Josephson scanning tunneling spectroscopy, we demonstrate that the single crystals of CsTi₃Bi₅ exhibit two distinct superconducting gaps. Furthermore, the superconducting gaps break the six-fold crystal rotational symmetry down to two-fold. At low energies, we find that the quasiparticle interference patterns exhibit rotational-symmetry-breaking C₂ patterns, revealing a nematic ordered normal state with the same nematic direction as in the superconducting state. Our findings uncover a novel superconducting state in CsTi₃Bi₅ and provide new insights for the intrinsic electron liquid crystal phases in kagome superconductors.