Observation of Electronic Nematicity Driven by the Three-Dimensional Charge Density Wave in Kagome Lattice KV3Sb5

Kagomesuperconductors AV(3)Sb(5) (A = K, Rb,Cs) provide a fertile playground for studying intriguing phenomena,including nontrivial band topology, superconductivity, giant anomalousHall effect, and charge density wave (CDW). Recently, a C (2) symmetric nematic phase prior to the superconductingstate in AV(3)Sb(5) drew enormous attention dueto its potential inheritance of the symmetry of the unusual superconductivity.However, direct evidence of the rotation symmetry breaking of theelectronic structure in the CDW state from the reciprocal space isstill rare, and the underlying mechanism remains ambiguous. The observationshows unconventional unidirectionality, indicative of rotation symmetrybreaking from six-fold to two-fold. The interlayer coupling betweenadjacent planes with pi-phase offset in the 2 x 2 x2 CDW phase leads to the preferred two-fold symmetric electronic structure.These rarely observed unidirectional back-folded bands in KV3Sb5 may provide important insights into its peculiar chargeorder and superconductivity.