Discovery of electronic nematicity in titanium-based kagome metal CsTi₃Bi₅

Rotation symmetry breaking of the electronic structure can in general be generated by structural anisotropy or electronic correlations via Coulomb repulsion. In kagome superconductors AV₃Sb₅ (A = Cs, Rb, K), rotation symmetry breaking appears to be intricately linked to the rotation symmetry breaking of the 2a0×2a0 charge density wave, leading to the formation of an orthorhombic phase. We use spectroscopic-imaging scanning tunneling microscopy (SI-STM) to discover an electronic nematic phase in the cousin kagome metal CsTi₃Bi₅. This electronic nematic state is characterized by rotation symmetry breaking in the electronic signal in the absence of any charge density wave phase reported in AV₃Sb₅. A comparison between the measured band structure and density functional theory calculations reveals notable differences at low energies, hinting at electronic correlations in CsTi₃Bi₅. The analysis of quasiparticle interference (QPI) patterns uncovers rotational symmetry breaking associated with titanium-derived d orbitals. Our work reveals a rare purely nematic electronic state on a hexagonal lattice that may be described by a three-Potts nematic order parameter.