Flat bands, non-trivial band topology and rotation symmetry breaking in layered kagome-lattice RbTi₃Bi₅.

Abstract

A representative class of kagome materials, AV₃Sb₅ (A = K, Rb, Cs), hosts several unconventional phases such as superconductivity, [Formula: see text] non-trivial topological states, and electronic nematic states. These can often coexist with intertwined charge-density wave states. Recently, the discovery of the isostructural titanium-based single-crystals, ATi₃Bi₅ (A = K, Rb, Cs), which exhibit similar multiple exotic states but without the concomitant charge-density wave, has opened an opportunity to disentangle these complex states in kagome lattices. Here, we combine high-resolution angle-resolved photoemission spectroscopy and first-principles calculations to investigate the low-lying electronic structure of RbTi₃Bi₅. We demonstrate the coexistence of flat bands and several non-trivial states, including type-II Dirac nodal lines and [Formula: see text] non-trivial topological surface states. Our findings also provide evidence for rotational symmetry breaking in RbTi₃Bi₅, suggesting a directionality to the electronic structure and the possible emergence of pure electronic nematicity in this family of kagome compounds.